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1990 Part 1     Front Cover (1990 - Part 1)    No author information available Summary: Not available         Table of Contents (1990 - Part 1)    No author information available Summary: Not available         Conference Information (1990)    No author information available Summary: Not available         Materials; What are the prospects? (superconductivity)    S. Tanaka Summary: Research activities of the Superconductivity Research Laboratory of ISTEC are summarized with emphasis on materials aspects. Particular attention is given to process research, thin films, high critical current materials, and tapes and wires. The outlook on future research and development in the field of high T/sub c/ superconductivity is also examined.         Flux motion and dissipation in high temperature superconductors    M. Tinkham Summary: An overview of flux motion and dissipation in high T/sub c/ superconductors is given. The author outlines aspects on which some consensus exists and then turns to questions which remain more controversial, describing the various experimental and theoretical approaches that have been adopted in probing the behavior of real superconductors. Some recent results on flux motion in SNS (superconductor-normal metal-superconductor) arrays are used to illuminate the duality between descriptions in terms of Josephson junctions and flux motion. It is pointed out that the high anisotropy of the YBCO-class materials and the extremely high anisotropy of the BSSCO class of materials stem from the key role of the strongly superconducting Cu-O planes in their structures.         Tunneling spectroscopy measurements on low-leakage junctions of Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ and Ba/sub 1-x/K/sub x/BiO/sub 3/    J.F. Zasadzinski, N. Tralshawala, Q. Huang, K.E. Gray and D.G. Hinks Summary: Tunneling measurements are reported for ND/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ (NCCO) and Ba/sub 1-x/K/sub x/BiO/sub 3/ (BKBO) using the point-contact technique with an Au or Nb tip. The junctions display very low zero-bias conductance values of <1% for BKBO and approximately 10% for NCCO and show sharp conductance peaks at eV=+or- Delta . In the case of BKBO, the normalized conductance can be fit with a BCS (Bardeen-Cooper-Schrieffer) density of states with thermal smearing only. The energy gaps are in good agreement with optical measurements and lead to values of 2 Delta /kT/sub c/ in the range of 3.5-4.0 for both compounds, implying moderate coupling strength. The tunneling conductance data at high bias voltages display reproducible structures which are characteristic of phonon effects as found in conventional superconductors. The Eliashberg functions were obtained, and the resulting values of lambda determined from this analysis are consistent with the measured values of the strong-coupling ratio, 2 Delta /kT/sub c/. It is concluded that the pairing mechanism in both materials is principally phonon mediated.         Scanning tunneling spectroscopic studies of superconducting NbN single crystal thin films at 4.2 K    S. Kashiwaya, M. Koyanagi, A. Shoji, M. Matsuda and H. Shibata Summary: A low-temperature scanning tunneling microscope (LT-STM) has been constructed to study the microscopic properties of superconductors. It has atomic resolution from room temperature to 4.2 K. Conductance spectra obtained between a Pt tip and a NbN thin film agreed well with theoretical curves based on the BCS (Bardeen-Cooper-Schrieffer) theory. This indicates that STM actually has the potential for probing the microscopic properties of superconductors.         High critical temperature superconductor tunneling spectroscopy using squeezable electron tunneling junctions    T. Walsh, J. Moreland, R.H. Ono, J.A. Beall, M. Cromar, T. Harvey, C. Reintsema and T.S. Kalkur Summary: Tunneling spectroscopy measurements were performed on squeezable electron tunneling (SET) junctions using Bi-Sr-Ca-Cu-O, Y-Ba-Cu-O, and Nb electrodes in a variety of combinations. A zero-bias conductance peak has been seen repeatedly in the current-voltage (I(V)) and the conductance-voltage (G(V)) characteristics. A model is presented to explain this conductance peak in terms of quasi-particle tunneling, phase diffusion, and a supercurrent. Two additional structures have been seen repeatedly in I(V) and G(B). One of these structures has the characteristics of an energy gap feature. The other structure, which can mimic the gap feature, is explained in terms of the switching to the voltage state of a grain boundary junction that is in series with the SET junction. The dependence of these features upon temperature and the force applied to the junction are examined.         Fabrication of Eu/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/ thin films and tunnel junctions by magnetron sputtering    H. Asano, H. Yonezawa, M. Asahi and O. Michikami Summary: Epitaxial Eu/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/ (EBCO) thin films have been grown in situ on SrTiO/sub 3/ and MgO (001) by DC magnetron sputtering from a stoichiometric sintered target. The controllable production of films with a particular orientation is found to be possible through the sputtering process. A high degree of crystalline quality for purely a-axis-oriented films on SrTiO/sub 3/ (001) is revealed by 4-axis gonio-X-ray diffraction and Rutherford backscattering spectrometry (RBS) study ( chi /sub min/ of 10% for 7-MeV /sup 4/He/sup 2+/ ion channeling). The zero-resistivity transition temperature obtained for completely a-axis-oriented film is 88 K, while it is 93 K for c-axis-oriented film. Tunnel junctions are fabricated using in situ deposited EBCO/Au/MgO/Nb structures and a photolithographic technique. The in situ grown, smooth films with the a-axis normal to the surfaces yield tunnel junctions which exhibit Josephson-like behavior. Critical current modulation is observed in response to an applied magnetic field.         Edge-geometry YBa/sub 2/Cu/sub 3/O/sub 7-x//Au/Nb SNS devices    B.D. Hunt, M.C. Foote and J. Bajuk Summary: The fabrication and electrical properties of edge-geometry YBaCuO/Au/Nb weak links are described. Superconductor/normal-metal/superconductor (SNS) devices of this type serve as sensitive probes of the electrical quality of the YBaCuO/Au interface. For device applications, the edge geometry has the advantage of placing the critical N/S device interface on the longer coherence length a-b surface, and it simplifies the fabrication of weak links with submicron dimensions. These structures are fabricated using laser-ablated, in situ, c-axis-oriented YBaCuO thin films, with both oxygen-annealed and unannealed YBaCuO/Au interfaces. The YBaCuO film edges are patterned using ion milling, followed by a low-energy-ion cleaning step and in situ deposition of Au and Nb. Devices with areas in the 10/sup -7/-10/sup -8/-cm/sup 2/ range have been fabricated with R/sub n/A products lower than 10/sup -8/ Omega -cm/sup 2/ and critical current densities up to 3 kA/cm/sup 2/. Josephson coupling is verified by the observation of microwave steps under 10-GHz microwave irradiation. The best results have been obtained with annealed YBaCuO/Au interfaces.         Major parameters of high T/sub c/ oxides    S.A. Wolf and V.Z. Kresin Summary: The major normal and superconducting parameters of several cuprate superconductors are evaluated and discussed. The effects of the two-gap structure in Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ are especially emphasized. It is pointed out that, for the two-gap superconductor such as Y-Ba-Cu-O, the analysis of the strength of the coupling should be carried out with considerable care. This is connected with the presence of three coupling constants, whose values can be entirely different.         The microwave surface impedance of high-T/sub c/ superconductors    H. Piel and G. Muller Summary: The available data on the microwave surface impedance Z/sub s/ of high-T/sub c/ superconductors from more than 30 laboratories around the world are reviewed to show the frequency, temperature, and field dependence of the surface resistance R/sub s/ and the temperature dependence of the field penetration depth lambda . The data are discussed on the basis of a two-fluid model and are compared with results from the classical superconductors Nb and Nb/sub 3/Sn. At temperatures above 0.8 T/sub c/, Z/sub s/ values of classical and high-T/sub c/ superconductors show strong similarities and are in close agreement with the Mattis-Bardeen theory. The comparatively very high R/sub s/ of the cuprates at 4.2 K, however, is indicative of a high density of unpaired charge carriers. The lowest values for R/sub s/ and lambda obtained until now with epitaxially grown YBa/sub 2/Cu/sub 3/O/sub 7- delta / films are 16 mu Omega at 4.2 K and 10 GHz and 140 nm, respectively. Such films are required for high RF field applications. Polycrystalline samples show a strong field dependence of R/sub s/. The highest magnetic surface field without R/sub s/ deterioration achieved so far on single crystals of YBa/sub 2/Cu/sub 3/O/sub 7- delta / is about 100 G.         Time-domain measurement of the surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting films up to 500 GHz    M.C. Nuss, K.W. Goossen, P.M. Mankiewich, M.L. O'Malley, J.L. Marshall and R.E. Howard Summary: The surface resistance and surface reactance of high-quality YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting films were determined from 10 GHz to 500 GHz using time-domain propagation measurements of picosecond electrical pulses on coplanar transmission lines. For the surface resistance, the authors find a square law dependence with frequency almost up to 500 GHz and a crossover of the losses of gold and YBa/sub 2/Cu/sub 3/O/sub 7/ films at 77 K at roughly 100 GHz. The pulse propagation is successfully modeled using the Mattis-Bardeen theory for the frequency-dependent conductivity of YBa/sub 2/Cu/sub 3/O/sub 7/. Good quantitative agreement of the surface resistance and surface reactance with this theory is obtained. The potential of YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting films and equivalent gold and superconducting films for high-speed applications is studied theoretically.         Surface impedance measurements of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films in stripline resonators    D.E. Oates and A.C. Anderson Summary: The microwave surface impedance of thin films of YBa/sub 2/Cu/sub 3/O/sub 7-x/ is measured as a function of temperature, frequency, and RF magnetic field, H/sub RF/, using a stripline-resonator technique. The films were deposited in situ by single-target off-axis magnetron sputtering. The frequency range was from 0.4 to 20 GHz, the temperature range from 4.2 K to T/sub c/, and the RF magnetic field range from 0 to 30 Oe. The surface resistance R/sub S/ at 4.2 K and 1.5 GHz is 4*10/sup -6/ Omega . The penetration depth is determined to be 0.167 mu m in the best film, In some films, R/sub S/ shows a linear dependence on H/sub RF/ and rises rapidly at large fields, showing no evidence of saturation. In others, R/sub S/ shows weak dependence on H/sub RF/ before rising rapidly. These behaviors differ from those observed in bulk ceramic YBa/sub 2/Cu/sub 3/O/sub 7-x/ and in unpatterned films measured in microwave cavities. However, the shape of R/sub S/(H/sub RF/) for the YBa/sub 2/Cu/sub 3/O/sub 7-x/ films is similar to that of Nb and NbN films measured in the same stripline geometry. The authors also present measurements of the intermodulation products in the resonators and discuss the implications of the R/sub S/ and intermodulation measurements for microwave device applications.         Measurements of the thickness dependence of the surface resistance of laser ablated high-T/sub c/ superconducting thin films    T. Kuhlemann and J.H. Hinken Summary: The authors report on measurements of the surface resistance of thin Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (TBCO) films made by laser ablation on SrTiO/sub 3/. Several films were prepared with thicknesses ranging from 100 nm to 400 nm. The surface resistance of these films was measured automatically in a temperature range from 20 K to 90 K using a copper cavity at 66.8 GHz. The measured values quantitatively show the expected temperature dependence of the effective surface resistance R/sub eff/ on the thickness of the superconducting films. From the measured R/sub eff/, one can calculate the true surface resistance R/sub ST/ by an analytical approximation which takes into consideration substrate losses and multireflections within the film. Results show that within the measurement uncertainty R/sub ST/ does not change with changing film thickness. At 77 K, R/sub ST/ values of about 15 m Omega were measured; at 30 K, R/sub ST/ reached 9 m Omega.         High-T/sub c/ thin films on low microwave loss alkaline-rare-earth-aluminate crystals    R. Sobolewski, P. Gierlowski, W. Kula, S. Zarembinski, S.J. Lewandowski, M. Berkowski, A. Pajaczkowska, B.P. Gorshunov, D.B. Lyudmirsky and O.I. Sirotinsky Summary: It is demonstrated that the alkaline-rare-earth aluminates (K/sub 2/NiF/sub 4/-type perovskites) are an excellent choice as the substrate material for the growth of high-T/sub c/ thin films suitable for microwave and far-infrared applications. The CaNdAlO/sub 4/ and SrLaAlO/sub 4/ single crystals have been grown by Czochralski pulling and fabricated into the form of (001)-oriented wafers. The Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O/ss films deposited on these substrates by a single-target magnetron sputtering exhibited very good superconducting and structural properties. Dielectric properties of the CaNdAlO/sub 4/ and SrLaAlO/sub 4/ crystals at submillimeter-wave frequencies are also presented and compared to measurements of materials most commonly used as substrates for deposition of high-T/sub c/ films. The comparison shows that SrLaAlO/sub 4/ is potentially the best material for millimeter-wave applications of high-T/sub c/ films because it combines excellent dielectric properties with a good lattice match with the Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O crystals.         High-frequency properties of Tl-based superconductors deposited onto large-area metallic substrates    D.W. Cooke, P.N. Arendt, E.R. Gray, A. Mayer, D.R. Brown, N.E. Elliott, G.A. Reeves and A.M. Portis Summary: Microwave surface resistance measurements were made on large-area (11.4-cm/sup 2/) Tl-Ba-Ca-Cu-O thick films/ss ( approximately 10 mu m) which were magnetron sputtered onto oriented Ag alloy (Consil 995) substrates. Initial films were prepared by depositing a BaF/sub 2/ buffer layer between the superconducting film and the substrate to control the film/substrate interaction; however, films exhibiting the best microwave properties were prepared without a buffer layer. Surface resistance measurements were made by replacing the end wall of an 18-GHz Cu cavity (TE/sub 011/ mode) with the superconducting film. The best surface resistance values obtained on the unbuffered film were 4 and 14 m Omega at 10 K and 77 K, respectively; the corresponding Cu values are 8 m Omega and 21 m Omega . The dependence of surface resistance on surface magnetic field was measured in a similar way except that an Nb cavity was used instead of a Cu one. Films exhibiting the highest degree of c-axis texturing show the weakest dependence of surface resistance on magnetic field and also exhibit the sharpest high-frequency transition into the superconducting state. These results are important for potential cavity applications of these materials.         Particle-induced modification of thin film YBa/sub 2/Cu/sub 3/O/sub 7- delta / transport properties and microwave device performance    D.B. Chrisey, J.S. Horwitz, H.S. Newman, B.D. Weaver, K.S. Grabowski, V.C. Cestone, M.E. Reeves, J.M. Pond and G.P. Summers Summary: The authors examine the modification of the microwave surface resistance (R/sub s/), the critical current (J/sub c/), and the critical temperature (T/sub c/) resulting from 2-MeV H/sup +/ and 12-MeV Si/sup 4+/ irradiation of high-quality thin films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / on <100> LaAlO/sub 3/ substrates. For both ions, the change in T/sub c/ (R=0) and J/sub c/ (77 K and 4.2 K) was roughly linear with fluence. The change in these properties with fluence was quantitatively similar once corrected for differences in the rate of energy loss to atomic displacements. R/sub s/ was also measured as a function of temperature for the same films at 36 GHz using the cylindrical cavity end-wall replacement technique. High quality c-axis oriented films exhibited sharp transitions in R/sub s/ near T/sub c/, followed by a relatively temperature-independent R/sub s/ with a value of approximately 6 m Omega at 20 K. For irradiation with H/sup +/ and Si/sup 4+/ ions, the sharp transition in R/sub s/ was shifted to lower temperatures, although below the transition temperature R/sub s/(T) was unchanged. The loaded quality factor, or Q, of a 5.3-GHz ring resonator, patterned from a 500-nm film on <100> MgO substrate, was measured as a function of temperature for 2-MeV H/sup +/ irradiation. While Q(T) was observed to decrease as a function of fluence, Q(T/T/sub c/) was invariant, as expected from the insensitivity of R/sub s/ to particle fluence below approximately 0.9 T/sub c/.         High T/sub c/ superconductor in an AC field    V.Z. Kresin Summary: The microwave properties of the high-T/sub c/ oxides are studied. The frequency and temperature dependences of the impedance are obtained. Short coherence length leads to large losses. The effects of impurities and multigap structures are discussed, and the impedance of the proximity system is calculated. The presence of the acoustic plasmon branch leads to intrinsic residual losses.         Bi-based high temperature superconducting tapes by cold rolling method    G. Kozlowski, C.E. Oberly, I. Maartense, R. Leese, J. Ho, D. Barker, T. Jones and T. Brown Summary: Bi-based high-temperature superconductor doped by lead with and without silver addition was used to produce tape approximately 1.2-cm wide and up to 20-cm long. Powder was calcined at 800 degrees C, 810 degrees C, and 835 degrees C for 50 h each time and loaded into silver tubes with o.d.=6.35 mm and i.d.=4.35 mm. Tapes with nominal thicknesses of 0.5 mm, 0.35 mm, and 0.2 mm were produced by the cold rolling technique. Direct transport current, DC magnetization, and AC susceptibility measurements were performed to characterize the superconducting properties of the tapes. The authors observed a significant increase in the magnetization critical current density with increasing number of calcinations and decreasing thickness of the tape, which is equivalent to the introduction of deformations into the system, thus increasing the number of pinning centers. A silver addition (3 wt.%) increases connectivity between grains and creates much cleaner grain boundaries.         Transport properties of Tl-Ba/Sr-Ca-Cu-O metal sheathed superconducting tapes in magnetic fields    K. Aihara, M. Okada, T. Matsumoto, S. Matsuda, F. Hosono and M. Seido Summary: Ag- or Au-sheathed taped with a Tl-Ba/Sr-Ca-Cu-O core were fabricated by a drawing-rolling and subsequent pressing method. The tape prepared at an optimized condition yielded a transport J/sub c/ of 15900 A/cm/sup 2/ at 77 K in the absence of a magnetic field, and 1100 A/cm/sup 2/ in a magnetic field of 1 T. The enhancement of J/sub c/ in a magnetic field was thought to be caused by an improved junction between grains and an unintentional introduction of a pinning center from various defects and unknown crystal phases. A 67-turn-pancake coil was made from a 10-m-long, 0.14-mm-thick and 2.5-mm-wide Ag-sheathed tape, which was capable of at least a 7-A critical current at 77 K in the absence of a magnetic field. The coil generated up to a maximum magnetic field of 103 G (a coil current of 3.0 A) without resistivity in liquid nitrogen.         J/sub c/-B characteristics of silver sheathed oxide superconductors    K. Shibutani, Y. Fukumoto, S. Hayashi, R. Ogawa and Y. Kawate Summary: Thermogravimetry, differential thermal analysis, and magnetization measurements on powders and silver-sheathed Y/sub 1-x/Ca/sub x/Ba/sub 2/Cu/sub 4/O/sub 8/ (x=0 and 0.1) were carried out. The deoxidation temperature of the Ca-doped Y124 materials in the silver-sheathed wires increased from 775 degrees C to 845 degrees C with increasing oxygen partial pressure (P/sub O2/) from P/sub O2/=0.2 bar (in air) to PO/sub 2/=1.0 bar (in pure oxygen). Although the critical transport current density of 2.1*10/sup 4/ A/cm/sup 2/ was observed for silver-sheathed Y(Ca)124 wire at 4.2 K and 0 T by selecting the oxygen partial pressure and the annealing temperature the grain boundary coupling was found to be inefficient by AC susceptibility measurement. A partial melting and growth technique was applied to silver-sheathed Bi2212 wires and well oriented and contacted grains aligned parallel to the silver wall were obtained.         Aspects of forming metal-clad melt-processed Y-Ba-Cu-O tapes    G. Kozlowski, C.E. Oberly, J. Ho and R. Leese Summary: The authors describe the manufacture of a tape of Y-Ba-Cu-O up to 25-cm long in nickel cladding using partial-melt processing. Magnetic and transport current measurements of the tapes were performed. Transport critical currents at 4.2 K of greater than 600 A have routinely been carried by these tapes. Magnetization measurements indicate that these high currents can be maintained up to 40 K. Aspects of selecting a criterion for establishing the transport critical current are discussed as they relate to applications.         Preparation of Y-Ba-Cu-O superconducting tape by pyrolysis of organic acid salts    I. Amemiya, H. Kobayasi, T. Nakamoto and T. Hasegawa Summary: A Y-Ba-Cu-O superconducting tape of 124 phase was successfully synthesized at atmospheric pressure by pyrolysis of organic acid salts. T/sub c(on)/=80 K and T/sub c(end)/=70 K were obtained along with a J/sub c/ of 2*10/sup 4/ A/cm/sup 2/ at 4.2 K and 0 T. An addition of calcium was found to elevate the T/sub c/ and improve the compactness of the film. The J/sub c/ of this sample is 3.2*10/sup 4/ A/cm/sup 2/ at 4.2 K and 0 T. The J/sub c/-B characteristic is better than that of the 124 phase without substitution.         Microfilamentary conductor based on Bi(2212)    T.A. Miller, L.A. Schwartzkopf, J.E. Ostenson, D.K. Finnemore, J. Righi, R.A. Gleixner and D. Zeigler Summary: A series of ex situ prepared microfilamentary conductors has been prepared to determine the optimum heat treatment sequence for the development of a strain-tolerant microfilamentary conductor based on Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub 8- delta /. Both monolithic tapes and the microfilamentary composites were prepared so that the difference between the two methods for the same heat treatment could be evaluated. The monolithic tapes are easy to fabricate and are used to provide a rough guide to the desired degree of melting and the optimum oxygen concentration needed for the highest critical current densities. One of the ex situ microfilamentary composites showed a critical current density of 5000 A/cm/sup 2/ at 4.2 K while subjected to a strain exceeding 1%.         High J/sub c/ YBCO superconductors prepared by the 'powder melting process'    Zhou Lian, Zhang Pingxiang, Ji Ping, Wang Keguang, Wang Jingrong and Wu Xiaozu Summary: A novel method called the powder melting process (PMP) has been developed to prepare high-J/sub c/ YBCO superconductors. The YBCO conductors have been fabricated through continuous zone melting and a unidirectional solidification process using precursor powders of Y/sub 2/BaCuO/sub 5/ (211) phase and Ba-Cu-O as starting material. The transport J/sub c/ values of the samples measured by a standard continuous DC four-probe method exceed 20000 A/cm/sup 2/ at 77 K, 4 T. A YBCO conductor with dimensions of 0.2-5*0.2-5*30-100 mm/sup 3/ can be fabricated by the PMP method. It is concluded that this approach will be potentially beneficial for fabricating oxide conductors with metal substrates since its melting temperature is lower than that of other melt processes by about 100 degrees C.         Microstructures and DC critical currents in textured Y-Ba-Cu-oxides    J. Orehotsky, H. Wisemann, A.R. Moodenbaugh, M. Suenaga, H.-G. Wang and H. Herman Summary: Sintered bars of Y-Ba-Cu oxide were partially melted using a quartz halogen lamp zone heating apparatus. The resulting multiphase samples showed varying degrees of melt texturing. It was found that the addition of YBa/sub 2/CuO/sub 5/ powders to the sintered YBa/sub 2/Cu/sub 3/O/sub 7/ prior to the zone melting process enhanced the growth of large textured grains. The best value of the critical current density was approximately 10/sup 3/ A/cm/sup 2/ at 1.0 T and 77 K for the starting composition of YBa/sub 2/Cu/sub 3/O/sub 7/-(0.2)Y/sub 2/BaCuO/sub 5/.         Crystallization of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ superconducting filaments produced by gas-jet fiberization    K.R. Jacobs, T.A. Miller, D.K. Finnemore, A.I. Goldman, S.E. Labeau and J. Righi Summary: X-ray diffraction and differential thermal analysis techniques have been used to investigate the recrystallization products obtained from various heat treatments of glassy Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ filaments produced by the gas-jet fiberization process. In both Pb-doped and Pb-free samples, the 85 K superconducting phase appears after the formation of a disordered Bi/sub 2/Sr/sub 2/Cu/sub 2/O/sub x/-like intermediate phase at lower temperature. The c-lattice parameter of this phase is substantially smaller than the published values for Bi/sub 2/Sr/sub 2/Cu/sub 2/O/sub x/ and increases as the temperature of the heat treatment increases. After heat treatment at 600 degrees C, a Pb-rich second phase is found together with the 2201-like intermediate phase in the Pb-doped material.         Evaluation of techniques for fabricating very fine grained YBa/sub 2/Cu/sub 3/O/sub 7- delta /+Ag composites    M.J. Kramer and S.R. Arrasmith Summary: The authors have compared several blending techniques to make Ag+YBa/sub 2/Cu/sub 3/O/sub 7- delta / (Y123) composites. A chemical precipitation route seems to give the best dispersion of the Ag but appears to cause some decomposition of the finer-grained fraction of the Y123. The lower intergranular porosity in these composites reduces the O/sub 2/ uptake in the samples, necessitating longer oxygen anneals. Long oxygen anneals for the composites can be avoided by first sintering the Y123 with an oxygen anneal and then blending in the Ag.         Effects of contact resistance between superconductor and stabilizer on stability in oxide-superconducting composites    K. Funaki, S. Funaba, M. Kobayashi, M. Takeo and K. Yamufuji Summary: The stability of superconducting composites of an oxide superconductor and a stabilizer with high electrical conductivity was studied theoretically in relation to contact resistance between the superconductor and the metal. The stability parameter of the minimum propagation zone (MPZ) was evaluated from an equilibrium distribution of temperature along the wire. Additional heat generation due to the contact resistance was induced around the normal zone and reduced the size of the MPZ. The relationship between the contact resistance and the stability was calculated numerically by a heat balance equation for the composite. A stability criterion for external disturbances was proposed as the condition for the size of the MPZ asymptotically approaching zero. This stability condition gives an upper limit on the current density as a function of the contact resistance.         High temperature superconductor joins    M.A. Hilal, X. Huang and J.D. Lloyd Summary: High-temperature superconductor (HTS) joint characteristics are different from low-temperature superconductor (LTS) joint characteristics due to the anisotropy of HTS current density. The critical state model can be satisfied in LTS joints along most of the interface region for all possible current transfer distributions. A critical state model is assumed for the HTS in which the current density has different critical values in the transverse direction, along the c-axis, and in the longitudinal directions, in the a-b plane: and losses are generated in the superconductor at currents lower than the critical current. A two-dimensional model is used throughout the analysis. It is shown that superconductor losses are likely to be generated in the lead joint for HTS conductors in the case of low J/sub cr/. This is due to limiting of the J/sub r/ to its critical value. This is not the case for an LTS conductor, since J/sub r/ is limited only by J/sub c/. For lap joints, the cross-sectional area for J/sub r/ flow does not change, and large superconductor losses will be generated only if the average interface current is greater than J/sub ct/.         Properties of YBa/sub 2/Cu/sub 3/O/sub 7- delta/ thin films grown on off-axis-cut MgO substrates    S.E. Russek, B. Jeanneret, D.A. Rudman and J.W. Ekin Summary: A series of YBa/sub 2/Cu/sub 3/O/sub 7- delta / films has been reactively sputtered on off-axis-cut MgO substrates. All the films were oriented with the c axis normal to the substrate regardless of substrate orientation, indicating that growth dynamics is a major factor influencing film orientation on nonlattice-matched substrates. As the substrate orientation was moved off the [100] direction, the films showed a decrease in transition temperature and showed properties indicative of an increased density of weak links. The films grown on high-angle substrates showed better properties than the films grown on low-angle substrates. Films grown on [110] MgO were as good as films grown on [100] MgO.         Characteristics of junctions made between Pb and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/    Y.F. Yang and J.E. Nordman Summary: Investigations of the junctions made between Pb and polycrystalline Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO) are reported. The BSCCO surfaces were treated with a number of methods, including mechanical scraping, plasma sputtering, plasma oxidation, and Br etch, before junctions were fabricated. The current-voltage characteristics and dynamic resistance (dV/dI) vs. voltage were measured at both 77 K and 4.2 K. The authors observed a Pb gap structure similar to that seen in Pb/YBa/sub 2/Cu/sub 3/O/sub 7- delta / junctions, a magnetic-dependent supercurrent, an asymmetric I-V curve, and narrow resistance peaks. Properties of junctions prepared in different manners are compared. Both X-ray photoemission spectroscopy and electrical studies indicated that Br etch is not suitable for the BiSrCaCuO system in spite of its successful application in YBa/sub 2/Cu/sub 3/O/sub 7- delta /.         Structural characteristics of grain boundaries in superconducting Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ fibers    S.C. Sanders, T.A. Miller, M.J. Kramer and L.S. Chumbley Summary: Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to study grain morphology and grain boundaries in superconducting Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ fibers produced by gas-jet fiberization. The narrowest fibers are composed of chains of platelets of about 52*3*0.2 mu m/sup 3/ oriented such that the long direction in each platelet is primarily parallel to the fiber axis. Each platelet has one crystallographic orientation. with the c-axis corresponding to the thin direction. These crystallites commonly join via large-angle (001) twist boundaries. where the ab-planes are parallel but rotated about the c-axis with respect to the next crystallite. More complicated boundaries are also observed. It is noted that it is not clear if having large-angle twist boundaries is a disadvantage in terms of achieving high critical current densities in these fibers. Twist boundaries may encourage a geometry where many crystallites can be stacked one atop the other, maximizing the overlap of the basal planes, which would allow the fiber to accommodate more current in the superconducting state.         Intergranular J/sub c/ determination in toroidal high temperature superconductors using a soft-core closed magnetic circuit    H.S. Lessure, S. Simizu, P.J. Kung, B.A. Baumert, S.G. Sankar and M.E. McHenry Summary: An examination of weak-link coupling between grains has been made using a noncontact magnetic technique. Intergranular J/sub c/(T) measurements for unaligned and grain-aligned sintered YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBC) toroids are reported. Supercurrent is deduced from measurement of the net current encircling the core, and J/sub c/ is found from supercurrent saturation in contrast to onset pickup voltage criteria. Agreement with recently reported direct transport measurements on the aligned sample suggests that the conduction mechanism is the same as for direct transport. A universal normalized J/sub c/(T) behavior which follows the same junction critical current temperature dependence previously reported in bicrystal transport measurements is found. It is proposed that this technique may be extended for the measurement of critical currents in thin-film samples and that present bulk intergranular current densities appear to be high enough to produce a soft-material limited superconducting electromagnet at 77 K.         Calculated stress distribution in a PbMo/sub 6/S/sub 8/ wire performing the I/sub c/ vs. epsilon experiment    W. Goldacker, C. Rieger and W. Maurer Summary: The precompression of the superconducting filament in a PbMo/sub 6/S/sub 8/ monofilamentary wire at 4.2 K. which was experimentally observed as a prestrain in an I/sub c/ vs. epsilon experiment, was simulated with the calculation of the thermal stress distribution using a triaxial elastic stress model. The occurrence of different prestress conditions, due to the choice of different barrier materials (Ta, Nb, and Mo) and as consequence of a varying reinforcing stainless steel content, was investigated by calculations and compared with experimental results. The change of the stress state in the filament with external axial stress shows a significant amount of hydrostatic stress even at the J/sub c/ maximum, which explains the observed degradation of superconductivity. For the presently used Chevrel-phase wire configurations with the unfavorable thermal expansion of the barrier materials, the hydrostatic stress component, e.g. the radial stress in the filament. is important for achieving a good bonding at the layer interfaces and creating the wanted prestress in the filament. If no alternative methods and materials for the barrier are found in the future, enhanced mechanical wire properties can only be obtained by a reduced layer thickness of the barrier, which would additionally improve the overall critical current density of the wire.         Intra- and intergrain critical current in PbMo/sub 6/S/sub 8/ sintered samples    D. Cattani, J. Cors, M. Decroux and O. Fischer Summary: To study the mechanisms limiting the critical current in the superconductor lead-molybdenum-sulfide, powders having a narrow distribution of T/sub c/ and B/sub c2/ have been synthesized. The absence of a broadening in the specific heat jump at the superconducting transition in a magnetic field indicates that the distribution of the critical field over the grains is very narrow. For all the samples, B/sub c2/ lies between 50 and 60 T (at T=0 K), whereas the critical current density displays a sharp decrease at a pseudocritical field which can be half of the calorimetric value of B/sub c2/. This reflects the poor quality of the grain interfaces, which limits the intergrain critical current. On a cold-pressed sample, it was possible to determine the intragrain critical current, which is estimated to be one order of magnitude higher than the best intergrain value. Therefore, an appreciable improvement in critical current density is expected if good superconducting links between grains can be achieved.         Magnetization properties of a SnMo/sub 6/S/sub 8/ single crystal    L. Le Lay, T.C. Willis and D.C. Larbalestier Summary: The authors synthesized a single crystal of the high-critical-field compound SnMo/sub 6/S/sub 8/ to serve as a model of the superconducting behavior of Pb/sub 1-x/Sn/sub x/Mo/sub 6/S/sub 8/ in wires and bulk samples. Magnetization critical current densities were measured in fields up to 11 T at various temperatures from 3.1 to 7 K. The behavior of the single crystal was compared to that of bulk and wire samples as well as to oxide superconductors. Significant field-induced flux pinning is found to occur within a single crystal of SnMo/sub 6/S/sub 8/. It is suggested that these pinning centers are atomic-scale defects.         High critical currents in Y-Ba-Cu-O films on silicon using YSZ buffer layers    D.B. Fenner, D.K. Fork, G.A.N. Connell, J.B. Boyce, A.M. Viano and T.H. Geballe Summary: Exceptionally high-quality films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) were successfully grown epitaxially on Si (100) wafers with a buffer layer of yttria-stabilized zirconia (YSZ) using a fully in-situ pulsed laser deposition (PLD) process. Critical current densities of a 30-nm-thick film are 2*10/sup 7/ at 4.2 K and 2.2*10/sup 6/ at 77 K. Zero-resistance critical temperatures are about 87 K, the transition width is 1 K, and normal-state resistivity is 0.28 m Omega -cm at 300 K. X-ray diffraction phi scans indicate in-plane epitaxial alignment within 1.0 degrees and 2.0 degrees for YSZ and YBCO, respectively. Lattice constant and thermal expansion mismatches occur at both subsurface interfaces. causing strain cracks to occur in YBCO films thicker than about 50 nm. The Si surface preparation utilizes an oxide etch and hydrogen termination that is an essential step in the process. as is careful control of the deposition environment temperature and oxygen pressure. The crystal quality of YSZ buffer layers on Si is not degraded by decomposition reactions, as is YBCO directly on Si or SiO/sub 2/, and cube-on-cube orientation of the YSZ cubic fluorite on Si (100) surfaces can be made to occur very effectively.         Surface characterization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films supporting metallic and insulating overlayers    D.D. Berkley, P.R. Broussard and A.M. Ervin Summary: The interface between thin films of the YBa/sub 2/Cu/sub 7-x/ superconductor and metallic and insulating overlayers is studied using films prepared in situ by coevaporation employing ozone vapor oxidation. Thin layers of Y, Y/sub 2/O/sub 3/, and BaF/sub 2/ can be evaporated at various stages of the YBa/sub 2/Cu/sub 7-x/ cool-down process. The effect of the overlayers on the oxidation state of the superconductor copper signal can be assessed using X-ray photoelectron spectroscopy (XPS). It is shown that ultrathin Y overlayers are rendered inert with respect to an underlying YBa/sub 2/Cu/sub 7-x/ film surface by the application of a pure ozone flux at the surface during deposition. This is accomplished at ambient substrate temperatures and at the highest temperature used in the processing of the superconductor. The preparation of epitaxial or highly oriented Y/sub 2/O/sub 3/ barriers is thus possible without an apparent effect on the integrity of the high-T/sub c/ surface and. perhaps, the superconducting order parameter. The barrier can be applied at a high substrate temperature where the mobility of the evaporant is large and crystallinity and smoothness can be expected to be optimum. It is expected that these results applied to high-quality a-axis oriented films may allow the development of improved-quality planar high-T/sub c/ tunnel junctions.         YBCO thin films on sapphire with an epitaxial MgO buffer    A.B. Berezin, C.W. Yuan, A.L. de Lozanne, S.M. Garrison and R.W. Barton Summary: The authors have developed a process for growing as-deposited c-axis YBCO thin films on R-plane sapphire using an epitaxial buffer of electron-beam-evaporated MgO. The authors discuss the structural and electrical properties of these films and describe the process parameters necessary for epitaxial growth of MgO on sapphire. A subsequent YBCO deposition yields a superconducting film with high transition temperature and critical current. While the YBCO is fully c-axis oriented, plane epitaxy is poor and so is RF surface resistance. Work in progress on a step-edge YBCO junction on MgO is mentioned.         Photolithographically patterned thin-film multilayer devices of YBa/sub 2/Cu/sub 3/O/sub 7-x/    J.J. Kingston, F.C. Wellstood, D. Quan and J. Clarke Summary: Thin-film YBa/sub 2/Cu/sub 3/O/sub 7-x/-SrTiO/sub 3/-YBa/sub 2/Cu/sub 3/O/sub 7-x/ multilayer interconnect structures in which each in situ laser-deposited film is independently patterned by photolithography have been fabricated. The two key components necessary for a superconducting multilayer interconnect technology have been constructed: crossovers and window contacts. As a further demonstration of the technology, the authors have fabricated a thin-film flux transformer which is suitable for use with a superconducting quantum interference device (SQUID) and includes a ten-turn input coil with 6- mu m linewidth. Transport measurements showed that the critical temperature was 87 K and the critical current was 135 mu A at 82 K.         Large-area YBCO films for microwave applications    J. Talvacchio, M.G. Forrester, J.R. Gavaler and T.T. Braggins Summary: The authors have developed techniques for the in situ deposition of epitaxial YBCO films on 2-in-diameter wafers of LaAlO/sub 3/ (001) or alpha -Al/sub 2/O/sub 3/(1102) with an Sr-doped La/sub 2/CuO/sub 4/ (001) (LSCO) buffer layer. The inductively measured transition temperature varied within the values of 91.1+or-0.5 K across the surface of the LaAlO/sub 3/ wafer and 90.7+or-0.4 K across the buffered sapphire wafer. The epitaxial LSCO buffer layer acted not only as a barrier to diffusion of Al into the YBCO films, but improved the YBCO (005) X-ray rocking curve widths from 4 degrees for films grown on bare sapphire to 1.2 degrees for films on the LSCO-buffered sapphire. The typical buffer-layer thickness was 40 nm, although layers as thin as 4 nm appeared to be equally effective. The transport critical density was greater than 10/sup 6/ A/cm/sup 2/ at 77 K for films on buffered sapphire. At 8.8 GHz and 4.2 K, the RF surface resistance was lower than that of gold, indicating that the films on sapphire will be useful in large-area UHF applications.         Preparation of thin film high temperature superconductors    X.X. Xi, T. Venkatesan, Q. Li, X.D. Wu, A. Inam, C.C. Chang, R. Ramesh, D.M. Hwang, T.S. Ravi, A. Findikoglu, D. Hemmick, S. Etemad, J.A. Martinez and B. Wilkens Summary: Fundamental issues in preparing high-quality high-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films are addressed. The techniques of inverted cylindrical magneton sputtering and pulsed laser deposition are chosen as successful examples to illustrate how the key problems can be solved. The fabrication of YBa/sub 2/Cu/sub 3/O/sub 7-x//PrBa/sub 2/Cu/sub 3/O/sub 7-x/ superlattices where superconductivity in a single unit cell layer of YBa/sub 2/Cu/sub 3/O/sub 7-x/ was observed demonstrates the state of the art of thin-film deposition of high-T/sub c/ materials. Systematic variations of the deposition parameters result in changes of superconducting and structural properties of the films that correlate with their microwave and infrared characteristics.         Comparison of the critical current anisotropy in YBaCuO and BiSrCaCuO films    L. Schultz, B. Roas, P. Schmitt, P. Kummeth and G. Saemann-Ischenko Summary: Laser deposition using an excimer laser was used to prepare thin single-crystal YBa/sub 2/Cu/sub 3/O/sub 7-x/ and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (BSCCO) films on <100> SrTiO/sub 3/ and LaAlO/sub 3/ substrates. The CuO planes of the films are always parallel, and the c-axes are perpendicular to the film plane. The critical current density j/sub c/ was measured in the whole superconducting temperature range in magnetic fields up to 7 T as a function of the angle theta between the field direction and the c-axis. At 4.2 K, j/sub c/(B perpendicular to c) is almost field-independent (up to 7 T), and, at 7 T, it is about one order of magnitude larger than j/sub c/(B//c) for both types of superconductors. This anisotropy increases markedly with increasing temperature, also at lower fields, for the BSCCO films. It decreases for the YBaCuO films, as long as j/sub c/(B) is not limited by the irreversibility field, leading to a crossover point in j/sub c/(B) at 77 K, where below 2 T, j/sub c/(B//c) is even larger than j/sub c/(B perpendicular to c). The extremely high pinning force for the B perpendicular to c configuration is explained by an intrinsic pinning due to a periodic variation of the order parameter perpendicular to the CuO layers. At higher temperatures, planar defects which lie parallel to the c-axis like twin boundaries or stacking faults become effective for YBaCuO and lead to a reduced difference of j/sub c/(B//c) and j/sub c/(B perpendicular to c). The absence of these planar defects might be a reason for the very low j/sub c/(B//c) values in BSCCO films at higher temperatures, although the critical current density at 4.2 K and zero field (1*10/sup 7/ A/cm/sup 2/) can be very high.         In-situ sputtering of YBCO films for microwave applications    P.H. Ballentine, A.M. Kadin and D.S. Mallory Summary: RF magnetron sputtering from a single YBCO target onto a heated substrate ( approximately=700 degrees C) was used to obtain c-axis-oriented 1-2-3 films that are superconducting without a subsequent annealing or oxygenation step, with T/sub c/(R=0) as high as 88 K on MgO and LaAlO/sub 3/ substrates. This process uses an 8-in-diameter target in the sputter-up configuration, with a central grounded shield to eliminate negative ion bombardment. It can reproducibly and uniformly cover substrates as large as 3-in across at rates exceeding 1 AA/s. Maintaining film composition very close to stoichiometry is essential for obtaining films with good superconducting properties and surface morphology. Optimum films have critical currents of approximately=1 MA/cm/sup 2/ at 77 K. Measurements of microwave surface resistance based on a stripline resonator indicate low surface resistance for unpatterned YBCO ground planes, but excess loss and a strong power dependence in a patterned center strip.         Off-axis magnetron sputtering of YBCO films: the influence of atomic oxygen    A.C. Westerheim, L.S. Yu-Jahnes and A.C. Anderson Summary: It is pointed out that in situ off-axis magnetron sputtering of superconducting Y-Ba-Cu-O (YBCO) is the simplest method for producing high-quality thin films. However, the method is not completely understood and the properties of films can vary widely among similarly configured systems and even from run-to-run in a given system. The authors have performed a series of experiments aimed at understanding and controlling the off-axis sputtering process. Film properties such as lattice parameter, T/sub c/, and surface morphology were measured as a function of substrate temperature, oxygen pressure, and substrate position. A method to accurately measure the substrate surface temperature has been developed, thus eliminating this as an unknown parameter. Under certain conditions, good films can be deposited at oxygen partial pressures well below the Hammond-Bormann oxygen-pressure-vs.-temperature stability curve for superconducting YBCO, showing the importance of the generation of activated oxygen in the sputtering chamber. Optical emission has confirmed the presence of atomic oxygen. Additional studies of the oxidation of YBCO films in molecular and atomic oxygen generated by an electron cyclotron resonance plasma show that the presence of atomic oxygen creates an equivalent pressure more than two orders of magnitude greater than molecular oxygen at that pressure.         Comparison of Ba/sub 2/YCu/sub 3/O/sub 7- delta / films on NdGaO/sub 3/ and LaAlO    J.M. Phillips, M.P. Siegal, C.L. Perry and J.H. Marshall Summary: The authors have studied the properties of 100-nm films of Ba/sub 2/YCu/sub 3/O/sub 7- delta / (BYCO) grown on LaAlO/sub 3/ (100) and NdGaO/sub 3/ (100) by coevaporation of Cu, Y, and BaF/sub 2/ followed by a two-stage anneal ex situ. It is found that the structural properties of the films on both substrates are optimized when the maximum temperature of the anneal is 900 degrees C, while the superconducting properties are slightly better if the maximum temperature does not exceed 875/spl deg/C. Films on LaAlO/sub 3/ can tolerate a longer time at the maximum annealing temperature than films on NdGaO/sub 3/. Optimized BYCO films on NdGaO/sub 3/ have substantially worse electrical and structural properties than those on LaAlO/sub 3/. It is hypothesized that this is due to a reaction between Ga in the NdGaO/sub 3/ and at least one of the constituents of the, BYCO film, probably Y.         In-situ low-temperature growth of YBa/sub 2/Cu/sub 3/O/sub 7-x/ films by reactive coevaporation    H. Tsuge and N. Matsukura Summary: Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-x/ films were grown in situ by reactive coevaporation using a triple-hearth electron-beam gun system, in which a single electron beam is scanned over constituent metal sources. Superconducting properties were improved by using reactive oxygen species generated from an RF discharge during growth and cooling. Zero-resistance temperatures T/sub c/(R=0) of 86-91 K and critical current densities of around 10/sup 6/ A/cm/sup 2/ at 77 K were obtained over the entire MgO (100) substrate of 15*15 mm/sup 2/. The c-axis-, a-axis-, and (110)-oriented films were selectively grown on MgO (100), SrTiO/sub 3/ (100), and SrTiO/sub 3/ (110), respectively, in a wide substrate temperature range with a crystallization temperature below 500/spl deg/C. A film prepared on SrTiO/sub 3/ (110) exhibited T/sub c/(R=0)=80K even when the substrate temperature was as low as 475/spl deg/C.         In situ growth of high temperature superconductor thin films with evaporation techniques using an ozone jet    H.M. Appelboom, J.P. Adriaanse, A.W. Fortuin, H.I. de Groot, S.M. Verbrugh, G. Rietveld, G. Hadley, D. van der Marel and J.E. Mooij Summary: High-quality YBa/sub 2/Cu/sub 3/O/sub 7/ thin films were grown in situ on various substrates (SrTiO/sub 3/, Al/sub 2/O/sub 3/, and Si) using MBE (molecular beam epitaxy) techniques and an ozone jet. The yttrium and copper are evaporated from electron-gun sources and the barium is evaporated from a Knudsen cell. All sources are controlled by a single mass spectrometer feedback system to obtain the correct fluxes at high partial ozone pressures. During deposition, the partial ozone pressure at the substrate position is estimated to be 10/sup -3/ -10/sup -2/ mbar. The substrate holder temperature is 700 degrees C. The real substrate temperature is estimated to be lower than 650 degrees C. The films are analyzed with R(T), X-ray diffraction, and RBS (Rutherford backscattering) measurements. Scanning electron microscope photographs are taken of the surface. The best film so far is grown on SrTiO/sub 3/ and has a T/sub c.onset/ of 88 K and a T/sub c0/ of 80 K. One 200-nm-thick film grown on bare silicon has a T/sub c.onset/ of 88 K and a T/sub c0/ of 60 K. This film shows negligible superconductor-substrate interactions according to the RBS measurements.         Growth and properties of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on non-lattice-matched and polycrystalline substrates    B.H. Moeckly, D.K. Lathrop, S.E. Russek, R.A. Buhrman, M.G. Norton and C.B. Carter Summary: The authors have investigated the nature of the in-situ growth of c-axis normal YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on non-lattice-matched, vicinal, and polycrystalline MgO substrates and on buffer layers of MgO. It is found that the preparation of the MgO surface determines the structural and transport properties of the films. In particular, the authors were able to reproducibly grow films exhibiting either weak link behavior or very high critical current densities. The variation of the thin-film microstructure, oxygen content, and superconductive properties with the changes in the thin-film crystal structure that result from the different growth situations is discussed. The structural and transport measurements of YBCO films grown on various MgO surfaces clearly indicate the importance of obtaining a nucleation stage which will result in high-quality YBCO on non-lattice-matched substrates. Such considerations are of prime importance when the low-temperature growth of the cuprate superconductors is required in order to obtain a morphology which facilitates the use of lithographic processing and the growth of multilayer structures.         Flux creep and flow in YBa/sub 2/Cu/sub 3/O/sub 7/ epitaxial films: role of planar defects    V.M. Pan, G.G. Kaminsky, A.L. Kasatkin, M.A. Kuznetsov, V.G. Prokhorov and C.G. Tretiatchenko Summary: The resistive state behavior for YBa/sub 2/Cu/sub 3/O/sub 7/ epitaxial films deposited by laser ablation onto SrTiO/sub 3/ (100) single crystals has been studied. The I-V curves and R(H,T) have been measured. The dissipation processes and temperature and field dependencies of the elementary pinning force and pinning potential are shown to be adequately described by the spatially inhomogeneous superconducting order parameter model and the existence of easy flux slip channels. Such channels seem to be formed along planar defects and can be disclosed experimentally, depending on the direction of the acting force, along or across the defect plane. It is clear that in the second case the planar defects serve as pins and can result in significant enhancement of the vortex activation energy. It is suggested that this factor can be responsible for the difference between vortex activation energy values derived from magnetic moment relaxation experiments and the transport properties of high-temperature superconductors.         Effects of deposition rate and substrate temperature on the orientation and the growth of YBa/sub 2/Cu/sub 3/O/sub x/ thin films    J.Q. Zheng, X.K. Wang, M. Shih, S. Williams, J. So, S.J. Lee, P. Dutta, R.P.H. Chang and J.B. Ketterson Summary: The authors report in situ studies of film growth by sputtering using synchrotron X-rays. The structure and growth habit of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) thin films deposited on [100] SrTiO/sub 3/ in a miniature, faced-magnetron sputtering system have been investigated. A combination of the substrate temperature and the deposition rate determines whether the film grows along the a, c, or multiple axes. At low substrate temperatures and low deposition rates, the films grow preferentially along the a-axis, In contrast, higher substrate temperatures and high deposition rates favor c-axis-oriented film growth with some admixture of [220]. The X-ray diffraction peaks were monitored in real time, revealing that a-axis- and c-axis-oriented grains nucleated on the surface of the [100] SrTiO/sub 3/ between 625 degrees and 765 degrees C, although the volume fraction of each orientation was temperature dependent. The structural quality of the a-axis films is superior to that of the c-axis films. The best a-axis films (deposited at 685 degrees C) had a rocking curve width of 0.08 degrees , which is 10 times smaller than that for the c-axis films (deposited at 800 degrees C). A shift of the [007] and [200,] peak positions during deposition was observed. The shift in the [007] peak is larger than that for the [200] peak. Defects in the c-axis films were observed, not only at the interface between the film and the substrate, but also on the upper surface of the (final) film; the latter seems to be inherent and is more severe in the films considered.         Relaxation of magnetic shielding tubes of sintered YBCO    Wang Jingrang, Li Jianping, Yang Wanming and Zhou Lian Summary: Magnetic shielding properties have been studied for sintered YBaCuO tubes of different size. The maximal DC shielding field reached 3.7 mT. It is found that the total shielding effect is not simply additive for two tubes put together. The shielding effect depends on temperature and the position in the external field, and the trapping field was found to be damped linearly with the logarithm of time, exhibiting flux creep behavior. The average persistent current density was about 10/sup 2/ A/cm/sup 2/. The potential barrier was estimated to be 0.78 eV and 0.76 eV for weak-link region and grain, respectively, according to Anderson's model of thermal activation from the damping rate of persistent current.         Irreversibility line and flux flow noise in superconducting Nb-Ta    E.S. Otabe, T. Matsushita, T. Matsuno and K. Yamafuji Summary: It has been found that the critical current density, J/sub c/, in high-T/sub c/ oxide superconductors is reduced to zero at high temperatures and/or high magnetic fields even in a superconducting region. The irreversibility line was investigated in weakly pinned superconducting Nb-Ta with low T/sub c/ and was compared with that in oxide superconductors. Large flux flow noise with a peak around 0.3 Hz was observed in Nb-Ta specimens. The noise power integrated in the frequency range of 0.1-1.0 Hz had a sharp peak, when it was plotted against the magnetic field. The mechanism of such a characteristic noise is examined.         Self-similarity in the I-V characteristics of granular YBa/sub 2/Cu/sub 3/O/sub 7/    S.S. Bungre, S.M. Cassidy, A.D. Caplin, N.M. Alford and T.W. Button Summary: The onset of dissipation in the I-V characteristics of granular YBa/sub 2/Cu/sub 3/O/sub 7/ shows clear evidence for a finite critical current. At currents above critical, dissipation in the weak links is only slightly field and temperature dependent. This self-similarity of the characteristics implies strongly that there is a true critical current, despite the random network nature of these materials. Also, it indicates that the dissipative behavior of the grain boundary weak links is almost field and temperature independent.         The observation of a transverse voltage at the superconducting transition of thin films    T.L. Francavilla and R.A. Hein Summary: The authors have observed the occurrence of a nonHall transverse voltage in the absence of any externally applied magnetic field as a film is brought through its superconducting transition either by changing temperature or current. This voltage goes from zero to a maximum and then back to zero as the transition is traversed in either direction. A model that accounts for these observations has been published by L.I. Glazman (1986). The experimental functional dependence of V/sub T/ is in good qualitative agreement with Glazman's theoretical predictions. This suggests that vortex-antivortex interactions, present in the mixed state of all superconductors, may be the cause for the observed nonzero V/sub T/. An orientational effect consistent with flux guiding which affects the amplitude of the observed peak and provides all explanation for the variation in amplitude has been observed. It is suggested that reports of anomalous Hall effect and resistance anomalies in the literature may be related to this effect.         Flux pinning in neutron irradiated YBa/sub 2/Cu/sub 3/O/sub 7-x/    H.S. Lessure, S. Simizu, B.A. Baumert, S.G. Sankar, M.E. McHenry, M.P. Maley, J.R. Cost and J.O. Willis Summary: Identical polycrystalline samples of YBa/sub 2/Cu/sub 3/O/sub 7-x/ have been irradiated with fast neutrons (E>0.1 MeV) in eight steps between 0 and 2.1*10/sup 18/ n/cm/sup 2/. Notable irradiation effects include a T/sub c/ depression of nearly 2 K at the highest fluence and large improvements in the critical current density for fields from 0-9 T and temperatures from 4-80 K. Critical currents approaching 2*10/sup 7/ A/cm/sup 2/ are observed for optimally irradiated materials at 5 K (in zero field), while at 77 K J/sub c/(0 kOe) approaches 5*10/sup 5/ A/cm/sup 2/. Irradiation is seen to take a nearly equilibrium magnetization curve at 77 K and broaden it to a significantly hysteretic curve. A substantial shift in the effective pinning potential as a function of current density is inferred from magnetic relaxation measurement at H=1 T. This is the first such measurement in which systematically increased activation energies for flux creep (as a function of current density) are noted.         Shielding and flux trapping properties of high temperature superconductors in the shape of hollow cylinders    U.E. Israelsson and D.M. Strayer Summary: Allowing for a field-dependent critical current density, the authors calculate the magnetic field that can be supported by hollow cylinders of varying wall thickness. An adiabatically stable field of 1.0 T can be shielded by or trapped in a cylinder with a wall thickness of 0.4 cm if the critical current density varies linearly with magnetic field and has a value of 10/sup 4/ A/cm/sup 2/ at a field of 1.0 T. Such a current density appears to be within reach of present state-of-the-art melt-processed YBa/sub 2/Cu/sub 3/O/sub 7/ (123) materials.         Flux creep in Josephson junction arrays    S. Pace, A. Saggese, R. De Luca, F. Celani and L. Liberatori Summary: In order to analyze the diamagnetic properties of weakly coupled structures in high-T/sub c/ ceramic superconductors , the Josephson junction array model is used. It is suggested that the coupling is strong enough to allow magnetic flux trapping inside nonsuperconducting regions surrounded by superconducting loops closed by Josephson junctions. It is noted that the presence of currents flowing through the junctions has to be taken explicitly into account in the Hamiltonian. This description leads to a creep model of the Josephson junctions array. As a result, one observes the following: (1) pinning centers generated by nonsuperconducting regions into the loops, (2) pinning potentials determined by fluxon motion barriers due to the Josephson junctions, (3) absence of degeneracy of the states corresponding to a different number of fluxons in the loops, and (4) a reduction of the barrier height due to measuring currents or to diamagnetic shielding currents. The last effect is equivalent to the Lorentz force effect in type-II semiconductors. Thus, it is believed that this picture greatly modifies the usual superconducting glass model.         Optically induced depinning and Josephson coupling in bulk Bi-Sr-Ca-Cu-O    W. Eidelloth Summary: Bridgelike constrictions were fabricated from polycrystalline bulk Bi-Sr-Ca-Cu-O (BSCCO), and their resistive transition was investigated as a function of temperature. DC current, magnetic field, and optical irradiation. The data are well described by a network of highly damped Josephson junctions. Evidence for optically induced depinning of vortices is presented. A threshold value was found for the product of current density and flux density, above which the resistivity increased linearly with applied magnetic field. This behavior is attributed to flux flow, and for conventional superconductors it is described by the Bardeen-Stephen relationship. It is shown that many electrical characteristics predicted by this model resemble flux creep.         Frequency dependence of AC susceptibility due to the viscous motion of flux lines    S. Takacs, F. Gomory and P. Lobotka Summary: The authors studied the influence of viscous flux flow on the field distribution and hysteresis losses in high-T/sub c/ superconductors with field-dependent critical current density J/sub c/. The results are compared with measurements of AC susceptibility on ceramic YBaCuO and BiSrCaCuO as well as on single-crystal YBaCuO samples. Clear evidence for flux flow effects is seen for frequencies above approximately 1 kHz for all samples. The extreme flux flow model indicates that the flux flow should play an important role at much lower frequencies. The deviations from these results could be caused to some extent by the field dependence of J/sub c/, but at lower frequencies the flux creep seems to be dominant. This is confirmed by the current-voltage characteristics of analogous samples. It is shown that some important differences appear in the frequency dependences of the real and imaginary parts of the AC susceptibility for fields of harmonic and triangular shape. These differences, as well as the weaker flux flow effects in BiSrCaCuO as compared with YBaCuO, offer support for the conclusion that the flux flow effects are generally less important than supposed by some theories.         The irreversibility line of (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ determined by DC magnetization    S.M. Green, C.J. Lobb and R.L. Greene Summary: The irreversibility line, H*(T), of c axis aligned B/sub 1.65/Pb/sub 0.35/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ is analyzed based on DC magnetization measurements for fields of up to 50 kOe. Its temperature dependence is found to be strongly based on the criterion used to determine irreversibility. Using sensitivity criteria of 5, 15, and 25*10/sup -5/ emu, the low field data fit H* approximately H/sub 0/*(1-T/T/sub c/)/sup 7/, with gamma approximately=2.3-2.6 and H/sub 0/* approximately 1.8*10/sup 4/ emu. Using fitted curves, the irreversibility line follows this equation over the entire field range with gamma approximately=3.2 and H/sub 0/* approximately 35*10/sup 4/ emu.         Flux creep in cation deficient Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub 8+d/    S. Nomura and Y.M. Chiang Summary: Flux pinning in Bi/sub 2/(Sr,Ca)/sub 3-x/Cu/sub 2/O/sub 8+d/ was investigated as a function of cation deficiency and thermal history. A comparison of polycrystalline samples of cation stoichiometric and highly alkaline earth deficient composition (x=0.3) shows a marked difference in the magnetization hysteresis ( Delta M) and time-dependent decay of magnetization at temperatures below 40 K. The pinning energy (95-140 meV at 10-20 K) derived from flux creep data for an x=0.3 cation-deficient composition is 4-7 times greater than that for a stoichiometric composition. The difference in Delta M between stoichiometric and nonstoichiometric compositions increases with increasing field out to 5.5 T and is greatest at 20 K, but still significant at 40 K. The intragranular J/sub c/ of an x=0.3 composition exceeds that of the stoichiometric by >10/sup 2/ at a field of 1 T. The dependence of pinning characteristics in cation-deficient samples on thermal history suggests that defect clustering or incipient precipitation plays an important role in improving pinning.         Time dependent critical state in disks and rings    H. Hemmes, A.R. Kuper and L.J.M. van de Klundert Summary: The authors have developed a model to calculate the response of the current distribution in disks and rings to a time-dependent applied magnetic field. In the model, the ring (or disk) is divided into concentric segments. The segments are assumed to be inductively coupled to each other and to the applied field. A time-dependent magnetic field induces a finite electric field in the ring/disk. The induced currents will then depend on the magnitude of the electric field and the current-voltage (I-V) characteristic. The current-voltage characteristic is modeled by a nonlinear resistivity. The currents determined from AC magnetization measurements on rings and experimental I-V characteristics are compared with the results of the proposed model. It is found that the shape of the magnetization curves can be easily reproduced. However, the frequency dependence of the current in the ring shows a discrepancy. The experimental frequency dependence of the currents is much smaller than that expected on the basis of the I-V characteristics and the model calculations. A possible cause could be inhomogeneities in the sample influencing the current distribution.         Thermally induced flux motion in grain aligned Y-Ba-Cu-O    K.G. Herd Summary: The flux-flow-induced Nernst effect was studied in grain aligned polycrystalline Y-Ba-Cu-O. Nernst voltages have been measured for magnetic fields up to 6 T and temperatures ranging from 75 K to 100 K. The observed behavior is similar to that seen in low-temperature superconductors. The linear temperature dependence of the Nernst voltage on the applied temperature gradient has been verified. The flux-flow resistivity has been measured in magnetic fields up to 6 T. The broadening of the transition curve with increasing applied fields is evident. The resistivity is approximately five times higher than that measured in a high-quality single crystal. The increase may be attributable to intergranular effects. The measured Nernst voltages and flux-flow resistivities have been used to calculate the flux-line transport entropy. A comparison with the transport entropy derived from single-crystal data indicates that the polycrystalline transport entropy is a factor of 5 smaller. The discrepancy may be related to the intergranular resistivities which are not flux-flow-induced, leading to an artificial suppression of the flux-flow viscosity and the calculated transport entropy.         Observations of vortex structure in YBa/sub 2/Cu/sub 3/O/sub 7/    H. Muller, H.J. Wiesmann and M. Suenaga Summary: The remnant magnetic flux distribution in a single crystal and a sintered polycrystal was examined using the magnetic particle decoration technique. The single crystal, which was heavily twinned, showed only local order in the flux lattice. This was probably due to lattice distortions caused by interaction between twin boundaries and fluxons. In the polycrystal, flux pinning effectiveness was seen to vary significantly between grains, depending on size and orientation. Grains with the c axis nearly perpendicular to the applied magnetic field were most effective at pinning flux. Some features of the decoration patterns implied that the flux distribution was influenced by more than just the grains at the sample surface.         Critical currents, magnetic relaxation and microstructure in zone-melted YBa/sub 2/Cu/sub 3/O/sub x/    D. Shi, J.G. Chen, M. Xu, W.H. Chen and K.C. Goretta Summary: Extruded YBa/sub 2/Cu/sub 3/O/sub x/ wires have been zone-melted to develop highly textured microstructures. The zone-melted wires exhibit large magnetic hysteresis and transport J/sub c/ values relative to conventional bulk YBa/sub 2/Cu/sub 3/O/sub x/. The transport J/sub c/ in the zone-melted wire, in magnetic fields up to 1.5 T, has been greatly improved at 77 K. Transmission-electron-microscope evidence suggests that this enhancement of J/sub c/ may be connected with small-angle grain boundaries. The magnetic hysteresis loop at 77 K in the zone-melted wire is largely increased relative to that for a sintered specimen. This increase in the hysteresis loop may possibly be attributed to a high density of dislocations acting as strong pinning centers.         Temperature dependence of the anisotropy in magnetic relaxation in YBa/sub 2/Cu/sub 3/O/sub 7-2/ thin films    S. Vitta, M.A. Stan and S.A. Alterovitz Summary: The relaxation of diamagnetic magnetization in the c axis aligned YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films is studied as a function of orientation and temperature in the range of 5-50 K at H=0.2 T. The magnetization M(T,H) in the orientations H//c and H perpendicular to c and at all the temperatures is found to decrease logarithmically with time t. The activation energy for the movement of flux lines U is found to be 30-110 meV in the range 5-50 K. For H//c, U increases continuously with T, whereas for H perpendicular to c, U has two apparent maxima: at T=10 K and T>50 K. These results are discussed in terms of the thermally activated flux motion model.         Viscous flux motion in anisotropic type-II superconductors in low fields    Z. Hao and J.R. Clem Summary: The Bardeen-Stephen model of viscous flux motion in isotropic type-II superconductors is extended to the anisotropic case characterized by a phenomenological effective mass tensor m/sub ij/. When the magnetic field is low and the vortex lines are aligned along one of the three principal axes, simple expressions for the viscosity tensor eta /sub ij/ of the viscous flux motion are obtained as functions of m/sub ij/ and the normal state conductivity tensor sigma /sub ij/ for temperature T close to the critical temperature T/sub c/. For the high-temperature oxide superconductors, the theory predicts that eta /sub b//sup (a)/: eta /sub b//sup (c)/: eta /sub c//sup (a)/ approximately=1:4 gamma :3 gamma /sup 2/, where eta /sub i//sup (i)/ is the viscosity for the motion along the i-axis of a vortex parallel to the j-axis and gamma = square root m/sub c//m/sub a/ is the anisotropy parameter (m/sub i/, i=a, b, c, are the principal values of the mass tensor satisfying m/sub a/ approximately=m/sub b/<         Current-limiting reactor based on high-T/sub c/ superconductors    Y.A. Bashkirov, L.S. Fleishman, T.Yu. Patsayeva, A.N. Sobolev and A.B. Vdovin Summary: It is pointed out that an inductance coil with the ferromagnetic core surrounded by a high-T/sub c/ ceramic shield is a highly nonlinear element in AC circuits and can find application as a current-limiting reactor. Such a reactor can function both by self-switching and external control. In the latter case, the transport current pulse can be an effective control. Experimental data are presented on shields of yttrium-barium ceramics with critical current densities of about 10/sup 6/ A/m/sup 2/ in a zero field at 77 K. An increase in J/sub c/ to 10/sup 7/ A/m/sup 2/ in a field up to 1 T is found, supporting the feasibility of current-limiting reactors based on high-T/sub c/ superconductors.         Measurement of transport critical current of Y-Ba-Cu-O using an inductive method    R. Spyker, G. Kozlowski and C.E. Oberly Summary: An inductive, contactless procedure discussed by E.A. Harris et al. (Cryogenics, vol.28, p.685-7, 1988) was used to measure two samples of Y-Ba-Cu-O one of which was conventionally sintered, the other prepared using a melt-processing technique. When made into ring form and placed as a tertiary winding on a transformer, the sample could be driven to the normal state and a critical current density determined. It was shown that the melt-processed material has a very large critical current density when compared with the conventionally sintered material, and it exhibits an instantaneous transition to the fully normal state at a well-defined current level. It was found that rapid degradation will occur in melt-processed Y-Ba-Cu-O if it is exposed to condensation after removal from the low-temperature environment. The critical current density invariably decayed during repeated experimentation from a level difficult to achieve with the equipment at hand, to a level not much above the non-melt-processed Y-Ba-Cu-O. The higher levels of measured critical current density could be restored with reoxygenation.         Is magnetic pinning a dominant mechanism in Nb-Ti?    L.D. Cooley, P.J. Lee and D.C. Larbalestier Summary: The authors compared the pinning behavior of an artificial pinning center (APC) composite and a nanometer-filament Nb 46.5 wt.% Ti composite to that of a conventional Nb 48 wt.% Ti composite. The microstructure of the APC composite resembles that of the conventional composite, where ribbons of normal metal form the pinning centers, whereas the nanometer-filament composite has no internal normal metal but pins at the filament surface instead. The APC composite exhibits much stronger pinning relative to B/sub c2/ than the conventional composite (21.4 GN/m/sup 3/. 7 T vs. 18.9 GN/m/sup 3/, 11 T), which is possibly due to the increased amount of pinning center (50 vol.% vs. 25 vol.%); however, the proximity effect reduces the B/sub c2/ unfavorably. In all three composites, F/sub p/ was proportional to (1-b)/sup 3/2/, which suggests that the magnetic interaction, rather than core pinning, dominates. F/sub p/ obeys a scaling relation as T tends to T/sub c/ in the conventional composite and over a wide range of temperature in the APC composite. In these regimes, one pinning body is also dominant, and it is suggested that pinning is done by clusters of pinning centers rather than by the individual pins.         Laser probing of high-T/sub c/ superconducting thin films    Yu.Ya. Divin, F.Ya. Nad', V.Ya. Pokrovski and P.M. Shadrin Summary: The spatial inhomogeneity of the electrical characteristics of high-T/sub c/ thin films was studied by optical laser probing. It was shown that the characteristic length L of inhomogeneous current distribution in high-T/sub c/ films may be much larger than the grain size a; for example, in polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ film with critical current densities j/sub c/(4.2 K) approximately 10/sup 3/-10/sup 4/ A/cm/sup 2/ and grain size a approximately 1 mu m, the characteristic length L was equal to approximately 15 mu m at T>T/sub c/ and approximately 100 mu m at T         Enhancement of critical currents in bulk and Ag-sheathed Bi(Pb)-2223 superconductors    D.J. Brauer, R. Eujen and J. Hudepohl Summary: The superconducting properties of the Bi(Pb)-2223 phase have been optimized. Prolonged annealing of coarse powder raised the j/sub c/ in bulk samples to as high as 1100 A-cm/sup -2/ at 77 K. The temperature dependence between 96 and 4.2 K was studied, where j/sub c/ rose gradually from 120 to 2100 A-cm/sup -2/. T/sub c/ dropped from 107 K to 64 K in magnetic fields up to 4 T, but decreased by only 1 K/T in higher fields. A tape prepared by rolling and subsequent annealing of Ag tubes containing Bi(Pb)2223 powder exhibited a j/sub c/ of 1700 A-cm/sup -2/ at 77 K and 11000 A-cm/sup -2/ at 4.2 K. The latter j/sub c/ dropped to 3000 A-cm/sup -2/ in a magnetic field of 0.25 T, but it was still 1200 A-cm/sup -2/ in a 10-T field. A tape fabricated by pressing a drawn and annealed wire proved to be less sensitive to low magnetic fields.         Considerations for practical conductor design of Chevrel phase wires    B. Seeber, P. Herrmann, L. Schellenberg and J. Zuccone Summary: It is noticed that the application of PbMo/sub 6/S/sub 8/ (PMS) wires for the generation of steady-state magnetic fields in excess of 20 T requires that several conditions be fulfilled in order to be realistic. Practical design considerations for PbMo/sub 6/S/sub 8/ wires are reported. Besides the availability of wires with sufficient lengths and uniform high critical current density J/sub c/, thermal and mechanical stability have to be achieved. The most severe criterion for thermal stability is based on the prevention of flux jumps in the presence of screening currents in the adiabatic limit. This results in filament diameters between 710 mu m and 90 mu m for critical current densities of 5*10/sup 8/ A/m/sup 2/ and 2*10/sup 9/ A/m/sup 2/, respectively. A dynamic stabilization of a PMS wire in an epoxy-impregnated coil is not very efficient. The behavior of the J/sub c/ of PbMo/sub 6/S/sub 8/ wires under tensile and compressive stress is discussed.         Current carrying properties of the HIP treated Mo-sheath PbMo/sub 6/S/sub 8/ wires    H. Yamasaki, M. Umeda, Y. Kimura and S. Kosaka Summary: The effect of HIP (hot isostatic pressing) treatments on the critical current densities of Mo-sheathed PbMo/sub 6/S/sub 8/ wires was investigated. Remarkable J/sub c/ enhancement was observed for the wires HIP treated at 1200 degrees C: J/sub c/>3*10/sup 8/ A/m/sup 2/ (8 T) has been frequently observed, and the best values were J/sub c/=2.2*10/sup 8/ A/m/sup 2/ (18 T) and 9.3*10/sup 7/ A/m/sup 2/ (23 T). Large J/sub c/(//)/J/sub c/( perpendicular to ) ratios, greater than 3, were observed for the wires with high J/sub c/, which demonstrates that the observed J/sub c/ enhancement is due to the improved interconnectivity between the PbMo/sub 6/S/sub 8/ grains. The prospect of using the HIP-treated Mo-sheath PbMo/sub 6/S/sub 8/ wires as a superconducting wire for extremely high-field magnets is discussed.         Critical currents in Pb/sub 1.2-x/Sn/sub x/Mo/sub 6/S/sub 8/ wires    G. Rimikis, W. Goldacker, W. Specking and R. Flukiger Summary: Increased critical current densities J/sub c/ up to 2*10/sup 4/ A/cm/sup 2/ at 4.2 K and 20 T were found for quaternary Chevrel-phase Pb/sub 1.2-x/Sn/sub x/Mo/sub 6/S/sub 8/ wires. Compared to the ternary compounds, the composition was varied over the whole mixing range, and the change of the crystal structure parameters T/sub c/ and J/sub c/ was analyzed and discussed with respect to the observed J/sub c/ enhancement. These results were obtained for different wire preparation techniques using unreacted or HIP (hot isostatically pressed) prereacted starting materials, but always the same current-stabilized (Cu) and steel-reinforced wire configuration. A very good reproducibility of the J/sub c/ values indicates homogeneous material properties of the filaments and a uniform wire cross section.         Development of in-situ second phase pinning structure in niobium-titanium based superconducting alloys    J.M. Seuntjens and D.C. Larbalestier Summary: A niobium-based superconducting alloy which has a rare-earth second phase that segregates between the matrix dendrites during solidification has been developed. The second phase can be refined by conventional deformation without heat treatment so as to form an in-situ fiber network. In such an alloy, one has independent control of the second-phase volume fraction as well as the matrix composition. The development of the in-situ alloy along with early microstructural and critical current results on the first wires are reported. The in-situ second phase was found to be about 2- mu m thick and 8- mu m apart in a conventionally solidified 35Nb-50Ti-15Y alloy. This size and spacing are suitable for producing a flux line lattice (FLL) pinning morphology in the strain available in conventional conductor processing. The properties of the test alloy are shown to be satisfactory with respect to easy melting, high ductility, and nondegraded superconducting properties.         Superconducting properties and microstructures in NbTi superconducting wires    K. Matsumoto, M. Nakajima, Y. Tanaka and K. Osamura Summary: The effects of the variation of microstructures in NbTi superconducting wires on the superconducting properties are investigated. The microstructures of specimens having a high J/sub c/ were investigated. The relationship between critical current density and the final drawing strain is simulated based on the observation of microstructures, and good agreement with the experimental results is obtained. Results indicate that J/sub c/ tends to increase with increases in volume fraction.         Position and amplitude of proximity effect peaks in the magnetization curves of NbTi/Cu and NbTi/CuMn multifilamentary strands    M.D. Sumption, K.R. Marken Jr. and E.W. Collings Summary: The magnitude and position of proximity-effect-related magnetization peaks in the M-H loops of multifilamentary NbTi superconductive composites have been studied. M-H loops were taken at T=4.2 K as a function of field-sweep amplitude, H/sub M/, for several specimens. Three regimes emerge: (i) low field, where proximity effects are mainly shielding in nature; (ii) high field, where there are anomalous trapping effects: and (iii) an intermediate-field region, corresponding to a crossover between these two regimes. Correlations are made between these regimes and the specimen parameters H/sub C1,NbTi/ and H/sub p,NbTi/. A relationship is found between the magnitude of the maximum of the high-field magnetization and the breakdown field of the copper.         A theoretical comparison of the effects of the shape of the pinning potential and a distribution of pinning energies of the apparent pinning energy as measured by magnetic flux creep    D.O. Welch Summary: In the analysis of magnetic flux creep experiments, it is assumed that, at a given temperature, the pinning energy, which must be overcome by thermal activation, depends on the magnetic induction and its gradient by U(B, Delta B) equivalent to U/sub p/(B)(1-( Delta B/ Delta B/sub max/))/sup n/, where U/sub p/ is the pinning well depth and Delta B/sub max/ corresponds to the critical current density with no thermal activation. Customarily, n is assumed to be unity, and any unusual temperature dependence of U/sub p/ is then ascribed to a distribution of well depths. However, realistic assumptions about the shape of the pinning potential yield 3/2         Transport critical current densities in bulk Tl/sub 2/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ and polycrystalline-thin-film Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/    M.P. Maley, G.J. Vogt, D.S. Phillips, J.Y. Coulter, P.N. Arendt and N.E. Elliot Summary: The authors report investigations of the dependence of transport critical current density, J/sub c/, upon magnetic field, B, at 4, 64, and 75 K in a bulk ceramic sample of Tl/sub 2/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ and in a polycrystalline, textured thin film of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/. In ceramic samples of Tl-2223, the authors generally observe the double-step J/sub c/ versus B characteristic, in which J/sub c/ drops from its zero field value to a plateau reached at B approximately 100 Oe. The plateau region then extends to a higher field B*(T) beyond which J/sub c/(B) decreases monotonically. Plateau J/sub c/ (75 K, 1.0 T) values>300 A/cm/sup 2/ with B*(75 K) approximately 1.5 T were achieved. In these samples, a pronounced peak effect is observed in which J/sub c/(B) increases monotonically with increasing B for 100         Processing and grain boundary effects in Nd/sub 1-x/Ba/sub 2-x/Cu/sub 3/O/sub 7+d/ superconductors    R.W. McCallum and S.I. Yoo Summary: Nd/sub 1-x/Ba/sub 2-x/Cu/sub 3/O/sub 7+d/ samples have been prepared with sharp superconducting transitions, with careful attention given to the details of sample preparation. Two causes for broad samples have been observed. The first is sample inhomogeneity, which is more difficult to eliminate than in the YBa/sub 2/Cu/sub 3/O/sub 7/ case, and the second appears to be associated with site disorder within a homogeneous sample. Very reasonable intragranular critical currents have been obtained in a sample with a small amount of Nd substituted on the Ba sites, but it is not clear if the Nd plays a direct role in flux pinning. Intergranular critical currents are still quite low due to the large grain size in the high-temperature-processed material and the Nd-deficient layer on the grain boundaries.         Phase equilibria in La(Y)-Ba-Cu-O systems and growth of high-T/sub c/ superconductor bulk single crystals    G.A. Emel'chenko, N.V. Abrosimov, A.V. Bazhenov, V.M. Masalov, A.A. Zhokhov, P.A. Kononovich, G.Yu. Logvenov and S.S. Khasanov Summary: The isobaric phase diagrams of BaO(La/sub 2/O/sub 3/)-CuO-CuO/sub 0.5/ systems at a partial oxygen pressure of 0.021 MPa and the phase transition BaO/sub 2/ to or from BaO at oxygen pressure up to 2.1 MPa were studied. A flux method for growing bulk single crystals of YBa/sub 2/Cu/sub 3/O/sub 7- delta /, La/sub 2/CuO/sub 4/, (LaSr)/sub 2/CuO/sub 4/, Nd/sub 2/CuO/sub 4/, and (NdCe)/sub 2/CuO/sub 4/ has been developed using a rotatable crucible which ensures separation of crystals from the melt. The effects of temperature, oxygen pressure, and heat-treatment duration on the superconducting characteristics of the crystals were studied.         Improved superconductivity in BiSrCaCuO single crystals by lithium doping    Y. Fujiwara, S. Hirata, M. Nishikubo and T. Kobayashi Summary: The authors successfully grew Li-doped Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ single crystals by a self-flux method and systematically investigated effects of the doping on the crystallographic and superconducting properties. Tlie crystal exhibited a cleaved surface perpendicular to the c-axis. The length of the c-axis increased linearly with the nominal ratio of Li to Cu in the melt, in agreement with the secondary ion mass spectroscopy (SIMS) observation that the relative amount of Cu and Li in the crystals was changed. The superconducting properties were improved by Li doping. The onset temperature of superconducting transition rose in proportion to the nominal ratio of Li, while the zero resistance temperature had a peak of 86.3 K at a ratio of 50%. Measurements of the Meissner effect implied that the behavior was bulky. The superconducting properties of the high-T/sub c/ phase were also improved by Li doping.         Surface degradation of high T/sub c/ superconductors    Q. Lu, G.L. Larkins Jr., W.K. Jones, R.J. Kennedy and G. Chern Summary: Surface degradation studies of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ (123) and Bi-Sr-Ca-Cu-O (2223) superconducting ceramics were performed in N/sub 2/, Ar/sub 2/, O/sub 2/, wet and dry air. By using a novel noncontact room-temperature technique the time dependence of the surface impedance of both 123 and Bi-Sr-Ca-Cu-O bulk ceramics was measured from 100 Hz to 20 kHz. In humid environments, the rate of degradation is dependent on the humidity and appears to be unaffected by the carrier gas. The surface impedance change due to humidity follows a power law and does not appear to saturate at a final value. In environments without water present, the surface impedance follows an exponential curve of the form 1+e/sup -at/, where a is approximately 150 s. This implies that the surface of the ceramic is relatively stationary and that it is losing oxygen. Oxygen loss converts the surface from a highly conductive state to an insulating state. This implication is supported by electron spectroscopy for chemical analysis (ESCA) spectra of the exposed surface and freshly abraded or broken samples' interiors. In the ESCA spectra of the exposed surface, there is a lack of Cu-O bond peaks; in the center of the same sample the Cu-O peaks are present.         Crystal chemistry and properties of the defect phases YBa/sub 2-x/Cu/sub 3/O/sub y/    G. Plesch, F. Hanic, M. Jergel, V. Strbik, M. Majoros, M. Kedrova, B. Svecova, V.E. Shvaikovski, A.I. Novikov and M. Herkelova Summary: The V-A characteristics, with and without an outer magnetic field, the T/sub c/, the phase stability at high temperatures, the oxygen intercalculation capacity in different ambient atmospheres (pO/sub 2/=1 Pa, 4*10/sup 3/ Pa and 2*10/sup 4/ Pa), and the paramagnetic behavior of ceramic samples YBa/sub 2-x/Cu/sub 3/O/sub y/ were correlated with the chemical composition and the applied technology for synthesis of the defect phases. X-ray diffraction, thermogravimetry, electron paramagnetic resonance, and the four-point resistive method were used to study the structure, phase composition, and physical properties of the Ba-deficient YBa/sub 2-x/Cu/sub 3/O/sub y/ phases. Optimal superconducting properties and the lowest contamination of the system were found for the composition YBa/sub 1.95/Cu/sub 3/O/sub y/.         Pb,Cu)Sr/sub 2/(Y,Ca)Cu/sub 2/O/sub z/, new superconducting layered copper oxides    K. Sakuyama, T. Maeda, S. Koriyama, H. Yamauchi and S. Tanaka Summary: Single-phase ceramics of Pb-based layered copper oxides, (Pb/sub (1+x)/2/Cu/sub (1-x)/2/)Sr/sub 2/(Y/sub 1-x/Ca/sub x/)Cu/sub 2/O/sub x/ (x=0 approximately 0.35), were successfully synthesized in an oxidizing atmosphere in contrast to the case of Pb/sub 2/Sr/sub 2/(Y,Ca)Cu/sub 3/O/sub 8/. Superconductivity is observed for the samples containing appropriate amounts of Ca such that x>0.25 when annealed in air and then quenched into liquid nitrogen. As the Ca content, x, increases, the superconductivity transition temperature increases. The superconducting onset temperature of 65 K is measured for the multiphase samples with x=0.5.         Local atomic configuration and Auger valence electron spectra in BiSrCaCuO single crystals    Y. Fujiwara, S. Hirata, M. Nishikubo, T. Kobayashi, H. Nakayama and H. Fujita Summary: Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ (2212) and Ca-doped Bi/sub 2/Sr/sub 2/CuO/sub y/ (2201) single crystals were systematically investigated by Auger valence electron spectroscopy (AVES). In AVES measurements on two kinds of crystals, a drastic difference was observed in the spectral shape of Ca(2p,3p,3p) reflecting a difference in spin-orbit splitting induced by local atomic configuration in the vicinity of Ca atoms. Furthermore, a Ca(2p,3p,4s) spectrum appeared in both crystals, indicating that the real valence of Ca atoms deviates from +2 in the crystals. The results suggest that AVES is a promising probe for characterizing local atomic configuration and valence electron states of the constituent elements.         Flux compression measurements in sintered bulk Ba/sub 2/YCu/sub 3/O/sub 7/    U.E. Israelsson and D.M. Strayer Summary: Trapping of magnetic fields and subsequent flux compression have been realized in sintered bulk Ba/sub 2/YCu/sub 3/O/sub 7/ superconductors at 77 K. The field is trapped in two interconnected holes of 0.95-cm and 0.52-cm diameter, respectively. By inserting a superconducting plunger with a diameter of 0.93 cm into the larger hole, the trapped flux is compressed into the smaller hole, where the flux density is measured with a Hall probe. The ratio of the areas available for the magnetic flux before and after compression is 3.7. Deviations from this compression ratio are observed to increase as the trapped field is increased, demonstrating penetration of magnetic flux into the interior of the superconductor. Using a simple extension of the critical state model, the authors demonstrate how the flux compression technique can be used to test the validity of the model and also to calculate the critical current density of the superconductor directly from the measurements.         The synthesis of new phases related to YBCO by complete replacement of the chain copper sites    C. Greaves and P.R. Slater Summary: The extent to which new phases may be synthesized by the replacement of the chain Cu sites (Cu1) in the YBa/sub 2/Cu/sub 3/O/sub 7/ structure was examined. Several new phases have been prepared, and it is demonstrated that, for cations which preferentially substitute at this site, it becomes possible to prepare phases in which the Ba cations have been totally replaced by Sr, e.g. EuSr/sub 2/Cu/sub 2/NbO/sub 8/. All phases of this type are tetragonal, and, using Rietveld refinement techniques and powder X-ray diffraction data, it has been confirmed that the Nb occupies only the Cu1 position and adopts octahedral coordination in EuSr/sub 2/Cu/sub 2/NbO/sub 8/. Phases involving other substituting cations are also discussed. Superconductivity has not been observed in these phases.         High electric field transport of the epitaxial YBaCuO thin films    K. Asano, K. Sakuta and T. Kobayashi Summary: Hole-carrier transport in epitaxial (001) Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/ thin films under the application of a pulsed high electric field was investigated. In every current-electric field curve of the normal conduction, strong nonlinearity appeared: currents no longer increased as the electric field increased in excess of certain threshold values. Observed current saturation was much more exaggerated with increasing low-field mobility (at lower temperatures or with better-quality films). These new phenomena of the high-temperature superconductors are very similar to the hot-carrier transport well known in semiconducting materials. Comparisons of the threshold field intensity and electron temperatures of oxide superconductors and typical semiconductors were performed.         A comparison of the E-J characteristics of four NbTi superconducting composites at equivalent electric field levels from 10/sup -4/ to 10/sup -7/ V m/sup -1/    R.G. Jenkins, H. Jones, N. Killoran and W. Timms Summary: The four-terminal short-sample test used to measure the critical currents of commercial superconducting composites typically employ equivalent electric field levels of 10/sup -5/ and 10/sup -4/ V m/sup -1/ to specify the onset of the superconducting-resistive transition. The authors describe refinements to this technique that enable resolution of the transition at the 10/sup -7/ V m/sup -1/ level. The techniques allowing access to the very lowest electric field regimes are based on the measurement of the decay rate of current in a continuous loop of a superconducting composite in background field. Data on four samples of NbTi conductor are compared over the full electric field range available using the above method, illustrating the influence of composite geometry and matrix material on the detailed form of the E-J characteristic.         Constant E-J relation in the current induced resistive state of YBa/sub 2/Cu/sub 3/O/sub 7-x/    Y.S. Hascicek and L.R. Testardi Summary: Restoration of a resistive state between 4.3 K and T/sub c/ was investigated by exceeding the J/sub c/ of bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/. Unlike the case of low-T/sub c/ Type-II superconductors, where restoration of the normal state resistivity is obtained by exceeding J/sub c/ by a fraction of J/sub c/, a constant value of differential resistivity which was several to many times smaller than that of the normal state value was obtained. This constant E-J slope remained constant up to ten times the transport J/sub c/. This value was constant for a given sample between 4.3 K and T/sub c/. The normal state resistivity just above T/sub c/ and the constant differential resistivity value below T/sub c/ were different for each sample. Since the value of this slope did not change by temperature at ambient fields, the constant slope of the E-J curves is not due to field-induced flux flow but may be due to a peculiar inhomogeneity of J/sub c/ throughout the sample. This point is further proven by the constancy of this slope at temperatures between 4.2 K and T/sub c/ under applied magnetic fields up to 200 G. Two breaks in the E-J behavior were observed near T/sub c/ which are believed to correspond to the intergranular and intragranular J/sub c/s, with the high J/sub c/ in agreement with reported values obtained by magnetization. Microstructural results imply that the mechanism for the observed behavior may be weak-link-related.         Normal-state resistivity diagnostic for high-T/sub c/ superconductors    G.F. Dionne Summary: A resistivity versus temperature ( rho -T) model that had been applied successfully to the Li/sub x/Ni/sub 1-x/O system has been extended to the La/sub 2-x/Sr/sub x/CuO/sub 4/ and YBa/sub 2/Cu/sub 3/O/sub 7/ high-T/sub c/ systems by fitting rho -T data with quantitative accuracy. It may also serve as the basis for interpreting the varying slopes of multiphase superconductors. Calculated curves of a two-phase approximation fitted to reported experimental data show that the metallic slope ( delta rho / delta T>0 above T/sub c/) and the rho -axis intercept of the linear extrapolation are related to the electron hopping activation energy and carrier concentration and may also be used to estimate the volume ratio of effective superconducting phase to normal phase within a particular specimen. It is shown that normal phases cause increases in rho , but decreases in slope of rho (T)/ rho (300), and that metallic slopes may be achieved with less than 10% effective volume of superconducting phase.         Switching in high T/sub c/ superconductor current transport measurements    L.F. Goodrich, J. Moreland and A. Roshko Summary: It is pointed out that switching voltages can occur in four-wire current transport measurements of sintered high-T/sub c/ superconductors. These switching voltages are irreversible shifts in the voltage-current characteristic of the superconductor that result in multiple branches. The voltage along these branches can be very nonlinear as a function of current and can be positive or negative in polarity relative to the current direction. These voltages can interfere with the correct determination of resistivity and critical current density. Experimental data on unaligned sintered Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta / which illustrate the complex nature of the voltages and the confusion they can create are presented. Models based on weak links and H/sub c1/ and on other effects are discussed as are observations on NbTi and Nb/sub 3/Sn-based superconductors.         Tunneling stabilized magnetic force microscopy: prospects for low temperature applications to superconductors    J. Moreland and P. Rice Summary: A low-temperature STM (scanning tunneling microscope) was built with the aim of getting TSMFM (tunneling stabilized magnetic force microscopy) images of the flux lattice in superconductors. The STM has been operated in a cryogenic bathysphere cryostat. The bathysphere cryostat will allow measurements from 4 K to 300 K in the bore of a high-field magnet. The STM has been operated in two modes at low temperatures: the STM mode with a rigid tunneling tip, and the TSMFM mode with a flexible magnetic tunneling tip. Magnetic bit racks were imaged on a hard disk with submicrometer resolution in the TSMFM mode at room temperature with an Au-coated Ni-film flexible tip. The TSMFM contrast improved markedly with this type of tip versus thicker Fe-film tips used previously. Preliminary TSMFM images of a YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) film (T/sub c/=88 K) in a 50-mT field show that relatively large magnetic forces are acting on the flexible tip while scanning at 48 K.         Hysteretic critical intergrain transport current in superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ as a basis for new switching and data storage effects    K. Kwasnitza and C. Widmer Summary: In sintered polycrystalline high-T/sub c/ superconductors, intergrain I/sub c/ depends on the magnetic history of the sample because the intragrain screening currents contribute a hysteretic component to the total B field at the grain interfaces. Experimental results on hysteretic intergrain I/sub c/ are presented, and application-relevant aspects of this behavior are investigated. Programmable switching and data storage effects were experimentally verified on the basis of this hysteretic I/sub c/ using the remanent state of intragrain magnetization. In the remanent state, information can be stored in the grains and read out by the transport current. Different I/sub c/-values were found at the same B/sub a/ and the same intragrain M but different shapes of the intragrain flux density profiles. The time relaxation behavior of intergrain I/sub c/ was studied, and a large reduction of relaxation rate was found under certain field cycling conditions. This could be important for future electronic applications.         In-situ epitaxial growth study of Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub x/ films by ion beam sputtering on cleaved MgO substrates    J. Fujita, T. Yoshitake, T. Satoh, T. Ichihashi and H. Igarashi Summary: In-situ epitaxial growth of Bi/sub 2/(Sr/sub 0.6/Ca/sub 0.4/)/sub 3/Cu/sub 2/O/sub x/ films on cleaved MgO substrates was studied by ion beam sputtering. The crystallographic structures were analyzed by using in-situ reflection high-energy electron diffraction, a four-circle X-ray diffractometer, and a scanning electron microscope. While the epitaxial films on polished MgO substrates commonly showed the fourfold symmetry, the epitaxial films having the twofold symmetry were successfully grown on the cleaved MgO substrates, and the films contained two types of misoriented domains. The epitaxial relationship between these domains and then cleaved MgO substrates was such that the b-axis of each domain deviated approximately +or-13 degrees from (010)MgO where the cleavage steps ran along (100)MgO. The early stage of film growth corresponded to an anisotropic growth mode, and the step edges tended to be the nucleation site. The step edges seemed to play an important role in determining the twofold epitaxial relationship, where the incommensurate modulation tended to align its direction so as to avoid the step edges.         Bi-Sr-Ca-Cu-O film on sapphire grown by plasma-enhanced halide CVD    T. Kimura, H. Nakao, H. Yamawaki, M. Ihara and M. Ozeki Summary: Plasma-enhanced halide chemical vapor deposition (CVD) for Bi-Sr-Ca-Cu-O (BSCCO) thin film has been developed. Superconducting BSCCO films were fabricated on 3-in-diameter sapphire substrates without postannealing. The CVD apparatus has four source-gas generation cells in which source materials (BiCl/sub 3/, SrI/sub 2/, CaI/sub 2/, and CuI) are evaporated or sublimated by heaters. Source gases are carried to the deposition chamber with helium. Oxidizing gases are O/sub 2/ and/or H/sub 2/O. The total pressure in the deposition chamber was 0.1 torr, and the O/sub 2/ partial pressure was 0.01 torr. Deposition was at 2 AA/min. It was found that the superconducting BSCCO film could be deposited on sapphire substrates at less than 700 degrees C without a solid-phase reaction between the film and substrate and that plasma-enhanced CVD controlled the BSCCO phases even at 580 degrees C. RF-plasma enhancement resulted in as-deposited superconducting BSCCO films. The c-axis orientation of the films was perpendicular to the sapphire's (1102)-plane. The 700-AA-thick (2212)-phase BSCCO film showed that the resistive transition started at about 100 K and that the zero-resistivity temperature was 70 K. The critical current density was about 2.5*10/sup 6/ A/cm/sup 2/ at 10 K.         In-situ formation of BSCCO thin films by plasma assisted thermal evaporation    R.M. Silver, E.T. Ogawa, S. Pan and A.L. de Lozanne Summary: Thin films of the superconductor Bi-Sr-Ca-Cu-O (BSCCO) have been prepared by thermal evaporation in an evaporator featuring an RF-excited oxygen plasma generator. Formation of the 2212 phase is obtained in situ, as confirmed by X-ray analysis. The films require postannealing, however, in order to exhibit a superconducting transition. Specifically, postanneals are required to obtain critical temperatures of up to 75 K; 1330 Pa is the minimum annealing pressure. The authors report the study of the superconducting properties as a function of oxygen annealing pressure as well as a characterization of the oxygen plasma. An investigation of the surface morphology was performed using a force microscopy (AFM) and a tunneling microscopy (STM). The latter clearly shows terraces and steps with a height of 1.5 nm, or multiples thereof, corresponding to one-half of the c-axis lattice constant of the 2212 compound. The AFM, on the other hand, shows a drastic difference between as-grown and annealed films, even when the former are sometimes insulating.         Mechanisms controlling the in-situ formation and superconducting properties of Bi-Sr-Ca-Cu-O films    R.T. Kampwirth, J.M. Grace, D.J. Miller, D.B. McDonald, K.E. Gray, M. Reiten, M. Ascolese and H. Latvakoski Summary: The authors report on the in-situ formation of superconducting films of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ and Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ using composite-target sputtering with substrate temperatures, T/sub s/, significantly less than those required for postannealed films. Specifically, superconducting films of BSCCO 2212 and 2223 can be sputtered onto single-crystal MgO substrates by an in-situ processing technique with T/sub czero/'s as high as 64 K and a very pronounced c-axis orientation without the need for epitaxy. Bi loss in the films can be reduced by biasing the substrate negative or increasing the total system pressure. This should provide greater control over film properties and the possibility of sputter deposition at higher substrate temperatures to see if T/sub czero/'s close to bulk can be achieved. The microstructure generally reveals a smooth matrix, with submicron to micron-sized particles protruding from it. These particles increase in size and frequency with increasing T/sub s/ and appear to be a Bi-Sr-Ca-oxide mixture. It is suggested that oxygen resputtering of the film may play a role similar to that reported for YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO).         The effects of anneal time and cooling rate on the formation and texture of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ films    M.M. Matthiesen, J.M. Graybeal, T.P. Orlando, J.B. Vander Sande and D.A. Rudman Summary: The effects of anneal time and cooling rate on the formation and texturing of superconducting Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ (BSCCO) films were investigated. Samples were prepared by sputter-depositing amorphous BSCCO films, annealing them at 870 degrees C in flowing 20% O/sub 2/-80% Ar for 30, 60, or 180 min, and then cooling them. Two cooling rates were investigated: a fast cool of 80 degrees C/min and a slow cool of 9 degrees C/min. It was observed that effective coupling between superconducting 2212 grains occurs when films exhibit a minimum amount of (00l) texturing. The nucleation and growth kinetics are significantly different for the isothermal and cooling regimes of thermal processing. Consequently, anneal time and cooling rate play distinct roles in the achievement of the appropriate texture and microstructure in the films: longer anneal times increase the volume fraction of the 2212 phase, while slower cooling rates enhance grain growth and texturing. The mechanism by which 2212 grains are coupled within a film is not well understood. It is suggested that grain growth mechanisms and rates may determine the extent of coupling between grains.         Synthesis and superconducting properties of Tl-Ba-Ca-Cu-O films    S.H. Liou, V.K. Chan, F. Foong, W.Y. Lee, Y.S. Gou and T.M. Uen Summary: Tl-Ba-Ca-Cu-O superconducting films were synthesized by sputtering either from a single target or from two oxide targets in a symmetric configuration. Films were zero resistance T/sub c/ of up to 122 K were obtained after various postannealing treatments at 870-950 degrees C under an oxygen atmosphere. The composition of the films is not very homogeneous on the submicrometer scale. The critical current of these films at 77 K is in the 10/sup 3/-A/cm/sup 2/-10/sup 4/-A/cm/sup 2/ range, which is much smaller than that of films prepared on SrTiO/sub 3/ and LaAlO/sub 3/ substrates. The low critical current density in these films is probably due to the granularity in the films. The morphology, structure, and magnetic and superconducting properties of the films were studied. Films prepared by two different sputtering techniques have similar results which depend mostly on the film compositions and their annealing conditions. It is found that the induced magnetic flux in the film decreases rapidly with increasing temperature, indicating weak flux pinning.         High-J/sub c/ silver-sheathed Bi-based superconducting wires    K. Sato, T. Hikata, H. Mukai, M. Ueyama, N. Shibuta, T. Kato, T. Masuda, M. Nagata, K. Iwata and T. Mitsui Summary: Silver-sheathed BiPbSrCaCuO wires were fabricated using the powder-in-tube method. Critical current densities at 77.3 K were 4.7*10/sup 4/ A/cm/sup 2/ in a zero magnetic field, 3.1*10/sup 4/ A/cm at 0.1 T, and 1.1*10/sup 4/ A/cm/sup 2/ at 1 T. In liquid He, these wires can carry 1.03*10/sup 5/ A/cm/sup 2/ at 23 T. J/sub c/ and J/sub c/-B enhancements are due to grain-boundary improvements. Detailed investigation of J/sub c/-B characteristics in magnetic fields, especially increasing and decreasing fields, revealed that history effect behaviours caused by weak links disappeared with improvements of grain-boundary characteristics at both temperatures. It was observed that 1296 multifilamentary wires were capable of sustaining over 70% of J/sub co/ even after a strain of up to 0.66% repeated 10 times. Prototypes of coils and current leads were fabricated using 20-m-long wires. One coil showed critical currents of 54.2 A at 77.3 K and 367 A at 4.2 K. This coil generated a B/sub m/ of 142 G at 77.3 K and 876 G at 4.2 K. A prototype of a react & wind-processed coil was demonstrated using greater than 4-m-long multifilamentary wires, and it successfully produced enough magnetic field to rotate copper windings between steel cores.         Development of high-T/sub c/ superconductor wires for magnet applications    J. Tenbrink, M. Wilhelm, K. Heine and H. Krauth Summary: Bi-2212/Ag phi 1-mm round untextured wires have been produced with critical current densities of 1200 A/cm/sup 2/ at 77 K, 0 T and up to about 2.0*10/sup 4/ A/cm/sup 2/ at 4.2 K in magnetic fields beyond 20 T. In order to achieve this, a two-step annealing procedure is necessary with a partial melting of the wire core, the melt having a composition near Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 6+x/. On cooling, the Bi/sub 2/(Sr,Ca)/sub 2/Cu/sub 1/O/sub 6+x/ phase appears at 880 degrees C, as revealed by in situ XRD (X-ray diffraction) measurements. Long-term annealing at 840 degrees C leads to the transformation of this phase into the Bi/sub 2/Sr/sub 2/Ca/sub 1/ Cu/sub 2/O/sub 8+x/ phase. The alkaline earth cuprate (Sr,Ca) /sub 14/Cu/sub 24/O/sub approximately=40/ and CuO occur as major extraneous phases. Helically shaped samples yield a lower j/sub c/ between 3*10/sup 3/ and maximum 1.0*10/sup 4/ A/cm/sup 2/ at 4.2 K, 10 T. Cracks due to thermal expansion mismatch with the sample holder and remaining inhomogeneities along the wire are responsible for these lower values. From I-V curves measured at 4.2 K, n-values were determined to be 20 to 25 in the interesting very-high-field region beyond 20 T. Bi-2223/Ag highly textured thin tapes yield an appreciably higher j/sub c/ of 2.6*10/sup 4/ A/cm/sup 2/ at 77 K, 0 T. Temperature-dependent measurements of j/sub c/ as a function of magnetic field B yielded onset of significant flux creep above 20 K, limiting the range of application in magnet technology to the temperature range up to 20 K unless an additional more effective pinning mechanism is introduced.         Fabrication, current density and strain dependence of sintered, Ag-sheathed BiSrCaCuO (2212) single filament and multifilamentary tape superconductors    J. Schwartz, H. Sekine, T. Asano, T. Kuroda, K. Inoue and H. Maeda Summary: Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (2212) superconductors have been fabricated into silver (Ag)-sheathed single-filament, multifilament, and wire-in-tube (WIT) tapes. Calcining, annealing and sintering conditions have been studied to improve the critical current density J/sub c/(B, 4.2 K) at high magnetic field (B). The optimization is discussed, and resulting properties are related to the microstructure of the superconductor. Superconductor J/sub c/ approximately 1-5*10/sup 4/ A/cm/sup 2/ has been obtained in fields >20 T at 4.2 K in both single and multifilamentary tapes. The dependence of J/sub c/ upon mechanical strain ( in ) has been investigated. No prestraining of the superconductor occurred in any of the samples, most likely due to yielding of the Ag sheath. Although strain resistance was good in all samples, the WIT tapes were significantly more resistant than the single-filament tapes. For the single-filament tapes, in /sub irr/ approximately 0.24%, while for the WIT tapes, in /sub irr/ approximately 0.36%, where in /sub irr/ is the irreversible strain limit.         J/sub c/ characteristics of textured Bi-based oxide tapes    H. Kumakura, K. Togano, D.R. Dietderich, H. Maeda, J. Kase and T. Morimoto Summary: Critical current densities J/sub c/ have been measured by both the resistive and the magnetic methods at various temperatures and magnetic fields for grain-oriented Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x//Ag composite tapes which were prepared by the combined process of doctor blade casting and crystal growth from the partially molten state. At 77 K, J/sub c/ of the tapes was greater than 10/sup 4/ A/cm/sup 2/ in zero magnetic field. However, J/sub c/ at 77 K is very sensitive to an applied magnetic field due to the large flux creep. This sensitivity of J/sub c/ to the magnetic field is significantly reduced at lower temperatures such that J/sub c/'s of a practical level (approximately 10/sup 5/ A/cm/sup 2/) are obtained at fields above 25 T at 4.2 K. The textured tape has an anisotropy in J/sub c/ with respect to magnetic field direction. This anisotropy increases with increasing temperature. However, the anisotropy factor at 4.2 K is small (approximately 1.5) and should not limit practical application.         Preparation of the textured Bi-based oxide tapes by partial melting process    J. Kase, T. Morimoto, K. Togano, H. Kumakura, D.R. Dietderich and H. Maeda Summary: Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ textured tapes with an excellent J/sub c/ were prepared by doctor-blade casting and a partial melt process. A green tape, composed of Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ powder and an organic formulation, was laid on a silver foil and heat-treated. A highly textured microstructure was formed during slow cooling between 890 degrees C and 870 degrees C. X-ray diffraction and scanning-electron-microscope observation indicated that initially an oriented Bi/sub 2/Sr/sub 2/Cu/sub 1/O/sub x/ structure forms by growth from the melt, and it subsequently transforms to the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ phase. A grain alignment was significantly enhanced in the oxide layer with a thickness less than 20 mu m. Silver dissolved in the oxide from the substrate also plays an important role in the grain alignment by lowering the melting point of the oxide. The T/sub c/ of a tape could be increased to 89 K by quenching from 870 degrees C. The J/sub c/ was 1.3*10/sup 4/ A/cm/sup 2/ at 77 K, 0 T and 1.4*10/sup 5/ A/cm/sup 2/ at 4.2 K in a high magnetic field of 25 T.         Critical currents in Ag sheathed tapes of the 2223-phase in (Bi,Pb)-Sr-Ca-Cu-O    R. Flukiger, T. Graf, M. Decroux, C. Groth and Y. Yamada Summary: The critical current density of Ag-sheathed (Bi,Pb)-Sr-Ca-Cu-O tapes with thicknesses below 0.2 mm exhibiting the 2223 phase has been systematically studied for various compositions and oxygen contents of the surrounding atmosphere. Various sequences of the final thermochemical treatment leading to a textured structure were also examined. Conditions for obtaining a high degree of texturing in Ag-sheathed tapes were found, yielding J/sub c/ values up to 17.500 A/cm/sup 2/ at 77 K, 0 T. A major factor for the improvement of J/sub c/ by the present cold deformation approach was the thickness of the 2223 layer, which should be smaller than 20 mu m. Due to the large number of parameters involved in the optimization of this system and to the complex formation conditions, a substantial further increase of J/sub c/ in the 2223 phase is still expected. This is particularly important in view of the use of 2223 tapes at 4.2 K and at high magnetic fields.         Measurement of the surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7- delta/ by the use of a coaxial resonator    P. Woodall, M.J. Lancaster, T.S.M. Maclean, C.E. Gough and N.M. Alford Summary: The design and initial testing of a coaxial cavity for microwave surface resistance (R/sub s/) measurements on high-temperature superconductors are described. The cavity design is optimized so as to produce the maximum number of harmonic measurements using TEM (transverse electromagnetic modes), in order for accurate measurements of R/sub s/ versus frequency to be made. Results for R/sub s/ using 17 harmonics in the frequency range 1-20 GHz are presented. Initial measurements of the field dependence of R/sub s/ are also given. The results show that the frequency dependence of the ceramic material's R/sub s/ is not omega /sup 2/, as expected from BCS (Bardeen-Cooper-Schrieffer) and the London model. The results also show that R/sub s/ is dependent on even very-low-RF magnetic fields. There have been a number of possible explanations for this deviation from the BCS or London theories of R/sub s/.         Millimeter wave surface resistance measurement on high temperature superconductors using a liquid nitrogen cooled cavity    B.-L. Zhou and S.-C. Han Summary: An accurate, relatively convenient and economical method of evaluating surface resistance R/sub s/ of high-temperature superconductors has been developed. This method is based on a technique of replacing one end wall of a copper cylindrical cavity which resonates at a frequency of 50.9 GHz in TE/sub 011/ circular mode. Measurement at 50.9 GHz allows evaluation of high-quality samples whose R/sub s/ value at 10 GHz is even one order of magnitude lower than that of copper. The proper diameter of the cavity is suitable for measuring samples with an area of 1 cm/sup 2/, the usual area used in thin-film growth and device fabrication. The cavity and the sample to be measured were cooled by liquid nitrogen, whose vapor pressure could be reduced to obtain temperatures down to 65 K. The temperature dependence of the R/sub s/ value of RF-magnetron-sputtered TBCCO thick film on Ag substrate and RF-magnetron-sputtered YBCO thin film on LaAlO/sub 3/ substrate has been measured in the temperature range of 65-250 K. The R/sub s/ value of the thick film was 0.17 Omega at 77 K. The R/sub s/ value of the thin film dramatically decreases below 90 K and reaches 18 m Omega at 77 K, which is almost two times lower than that of oxygen-free, high-conductivity (OFHC) copper.         Dielectric waveguide resonator with a superconductive boundary layer    C.-L. Huang and D.P. Butler Summary: Dielectric waveguide resonators have been shown to exhibit high Q's, limited by the dielectric loss. High-resonator Q is desirable in measuring the microwave attenuation of superconducting materials. The properties of a dielectric waveguide resonator with a superconductive boundary layer have been investigated. The microwave properties of YBaCuO and NbN thin films have been investigated by employing them as boundary layers on the dielectric waveguide. Transmission and reflection measure measurements on the dielectric waveguide resonator were performed from 20-40 GHz using a vector network analyzer. The temperature dependence of the loaded Q of the resonator was measured under weak coupling. The loaded Q-factors of the DWG resonator were measured to be as high as 12000 with a YBaCuO boundary and 20000 with an NbN boundary layer. The measured Q-factors were instrumentation limited in the superconducting state and represent a lower bound on the Q of the resonators. The results were found to be in agreement with the predictions of the Drude model for T>or=T/sub c/ and the Mattis-Bardeen theory for T         Double gun off-axis sputtering of large area YBa/sub 2/Cu/sub 3/O/sub 7- delta / superconducting films for microwave applications    N. Newman, B.F. Cole, S.M. Garrison, K. Char and R.C. Taber Summary: In order to extend earlier work on in-situ off-axis sputtering to larger areas, the authors used two facing targets in the off-axis configuration to produce YBa/sub 2/Cu/sub 3/O/sub 7- delta / superconducting films with low microwave surface resistance on 5-cm-diameter LaAlO/sub 3/ substrates. Surface resistance (R/sub s/) values at 10 GHz of 40+or-10 mu Omega at 4.2 K and 400+or-100 mu Omega at 77 K, superconducting transition temperatures of over 89 K, and thickness variations of less than +or-8% are uniformly obtained over the entire 5-cm-diameter area. The authors also report a detailed characterization of the electronic and structural properties of the films produced on the LaAlO/sub 3/ substrates for a wide range of growth conditions. The influence of YBCO microstructure on the transport properties and the effect of magnet geometry in the two sputter guns are also discussed. It is concluded that in-situ off-axis sputtering from two facing targets can reproducibly fabricate very-high-quality YBCO films with low microwave surface resistance over large areas. The thickness uniformity over large areas is greatly enhanced over single-target sputtering by using this technique.         SAW measurements on a Nb film and an YBa/sub 2/Cu/sub 3/O/sub 7/ film    H.P. Baum, B.K. Sarma, M. Levy, J. Gavaler and A. Hohler Summary: Surface acoustic wave attenuation measurements have been performed in a screen room on a superconducting film of Nb at 659 MHz and on a high-T/sub c/ film of YBa/sub 2/Cu/sub 3/O/sub 7/ at 168 MHz. The attenuation in the Nb film is due to electron-phonon interaction and follows a BCS (Bardeen-Cooper-Schrieffer) curve in the superconducting state. The measured change in attenuation was 0.8 dB/cm, giving an electron mean free path which is about twice as large as the value obtained from the sheet resistivity of the Nb film. The sheet resistivity of the YBa/sub 2/Cu/sub 3/O/sub 7/ film was 45 Omega / Square Operator , and the observed change in attenuation at T/sub c/=87 K was 0.18 dB/cm. A percolation model is proposed for describing the behavior of both the attenuation and the sheet resistivity in the superconducting state. This model is also used to determine the minimum resistance of YBa/sub 2/Cu/sub 3/O/sub 7/ along the ab plane. It is found to be 12.5 mu Omega -cm.         Determination of surface resistance and magnetic penetration depth of superconducting YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films by microwave power transmission measurements    K.B. Bhasin, J.D. Warner, F.A. Miranda, W.L. Gordon and H.S. Newman Summary: A novel waveguide power transmission measurement technique has been developed to extract the complex conductivity ( sigma *= sigma /sub 1/-j sigma /sub 2/) of superconducting thin films at microwave frequencies. The microwave conductivity of two laser-ablated YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films on LaAlO/sub 3/ with transition temperatures (T/sub c/) of approximately 86.3 and 82 K, respectively, in the temperature range 25 to 300 K was determined. From the conductivity values, the authors calculated the penetration depth ( lambda ) to be approximately 0.54 and 0.43 mu m and the surface resistance (R/sub s/) to be approximately 24 and 36 m Omega at 36 GHz and 76 K for the two films under consideration. The R/sub s/ values were then compared to those obtained from the change in the Q-factor of a 36-GHz TE/sub 011/-mode oxygen-free, high-conductivity (OFHC) copper cavity by replacing one of its end walls with the superconducting sample. It was found that this technique allows noninvasive characterization of high-T/sub c/ superconducting thin films at microwave frequencies.         Laser-induced voltages in unbiased YBCO-dependence on crystalline anisotropy    H.S. Kwok, J.P. Zheng and S.Y. Dong Summary: The photogenerated voltage in YBCO films without any current bias was studied by characterizing the grain orientations of the film samples and correlating them to the signal. Contradictory results to earlier reports were observed. It was found that crystal anisotropy was important in producing the photoinduced voltage. The photovoltaic response is ultimately related to the anisotropy of the lattice and can be used to study the crystal structure of these perovskites. The physics of this effect is quite different from the normal photoresponse under current bias. The latter is generally much stronger, and both thermal and nonthermal responses have been demonstrated.         Multi-phase structure of thermally diffused niobium nitride    P. Fabbricatore, R. Musenich, M. Occhetto, R. Parodi, P. Pompa and F. Merlo Summary: In order to study superconducting niobium nitrides for RF applications, Nb-N samples obtained by diffusion of nitrogen in bulk niobium were investigated. X-ray diffraction and AC susceptibility measurements were performed. From these measurements, the composition and the critical parameters (H/sub c1/ and J/sub c/) of the material were deduced. The results for several samples are compared. It is shown that the proposed method allows detection of the presence of different superconducting phases and granularity of materials. It was used to understand the RF behaviour of Nb-N (high residual surface resistance). Although the measured samples did not show granularity, the presence of several materials with different superconducting properties was observed. Low-T/sub c/ phases were always detected in the samples, sometimes also at the surface.         Electron beam (EB) weldability study of Consil 995-a structural material for RE cavity applications of thin film high temperature superconductors    R.J. Sinko, H.G. Campbell, P. Arendt and N. Elliot Summary: An investigation of successful joining parameters for the silver alloy Consil 995 in connection with EB welding has been performed. The results have been obtained by metallographic inspection, mechanical testing, X-ray diffraction, and electron microscopy. The changes in material properties due to welding and heat treating are reported and compared to those for niobium. From metallographic and mechanical tests, it is recommended that forming and welding fabrication of Consil 995 be performed prior to oxidation hardening. When welded and oxidized, this alloy shows good strength in the base metal and welded regions. This fits well into the scheme of fabricating accelerating cavities as it allows the forming, joining, and oxidation of the cavities before the high-temperature superconductor film is deposited. It is noted that Consil 995 is readily EB welded. A smoother underbead with less root reinforcement is desired and could be achieved by investigating travel speed and focus parameters.         DC features and RF losses of Nb-based superconducting thin films    D. Di Gioacchino, P. Fabbricatore, S. Frigerio, U. Gambardella, R. Musenich, R. Parodi, G. Paterno, S. Rizzo and C. Vaccarezza Summary: Superconducting thin films of Nb, NbN, and NbZr have been realized in view of their application to superconducting accelerating cavities. The samples have been sputtered on different planar substrates, i.e., glass, sapphire, and copper. The electrical and superconducting features of the films have been measured in the temperature range of 300 K to 4.2 K and in the presence of a magnetic field of up to 5 T. The residual resistivity, critical temperatures T/sub c/, and upper critical fields H/sub c2/ of the films are reported. The expected RF properties are discussed. Measurements of the RF dissipation of Nb/sub 75/Zr/sub 25/ films sputtered on copper substrates have been performed in a cylindrical TE/sub 011/ cavity. For Nb/sub 75/Zr/sub 25/ thin films, the authors have measured the superconducting energy gap and the surface resistance in a cylindrical TE/sub 011/ cavity in order to compare the experimental value to the theoretical BCS (Bardeen-Copper-Schrieffer) computation result.         Surface impedance measurements and calculations according to the Mattis-Bardeen theory on high-T/sub c/ superconductors    N.D. Kataria, R. Popel, H. Wolf, H. Sachse, T. Kuhlemann and J. Niemeyer Summary: Surface impedance measurements made on YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films are reported and compared with the exact solution of the Mattis-Bardeen theory applied to strong-coupling superconductors. Epitaxial films of YBCO were grown by the coevaporation of Y, BaF/sub 2/, and Cu and ex-situ wet O/sub 2/ annealing. The films were deposited at substrate temperatures ranging from 200 degrees C to 820 degrees C. X-ray diffraction shows that the films grown in the temperature range 720 degrees C-780 degrees C are epitaxial with the c-axis perpendicular to the substrate surface. Surface impedances of the samples were measured using a cylindrical copper cavity at 66.8 GHz. It is demonstrated that the value of the surface resistance can be considerably reduced on c-axis-oriented epitaxial films with correlated a-b orientation across the whole surface of the film. The calculation of the surface resistance using the Mattis-Bardeen theory is found to explain the experimental behavior with Bardeen-Cooper-Schrieffer (BCS) energy gap value.         Exact solutions of the Mattis Bardeen theory for thin superconducting films and bulk material    R. Popel Summary: The Mattis-Bardeen theory describing the anomalous skin effect in superconductors is exactly solved for thin films and bulk material. When five material parameters (i.e., the energy gap, the critical temperature, the London penetration depth, the Fermi velocity, and the mean free path) are known, calculation of all frequencies, mean free paths, and temperatures can be carried out, leading to the determination of the surface impedance. The calculation agrees well with measurements of the quality factor on resonant cavities, absorption in bulk materials, and transmission through thin superconducting films in the microwave and in the far-infrared region. It is shown that the solution in the extreme anomalous limit cannot describe these measurements and that the Mattis-Bardeen theory describes measurements on strong-coupling superconductors well.         Microwave surface impedance in a coaxial cavity as a material characterisation technique    J.C. Gallop, W.J. Radcliffe, T.W. Button and N.M. Alford Summary: Measurements of the surface resistance R/sub s/ of a number of modes of a coaxial cavity for which the center conductor is a BiSrCaCuO (BSCCO) rod have been made. Results for R/sub s/(T) have allowed a quantitative estimate to be made of the proportions of two different phases present in this material. The variation of R/sub s/(T) with applied DC magnetic field has also been measured for fields below about 1 mT. The results are interpreted in terms of two simple models for microwave loss in bulk high-temperature superconductors. It is concluded that the measurement of microwave surface impedance for high-temperature superconducting specimens can be used to make quantitative estimates of the proportions of various discrete superconducting phases, provided each has a distinguishably different T/sub c/. The apparent concentration at the surface of the high-T/sub c/ phase, believed to be Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/, has not been previously reported and may have significance for applications of these materials.         Optimizing high frequency response of thin films deposited on composite substrates    M.E. Rizkalla, G.A. Girgis and M.M. Holdmann Summary: The authors consider the thermal limitations placed on the high-frequency response of a superconducting device (switch) composed of a thin film (YBa/sub 2/Cu/sub 3/O/sub 7/) deposited on magnesium, sapphire, or silver substrates. In applying successive current pulses to the film, the heat generated during the quench must be transmitted from the film (source) through the substrate and dissipated in the coolant bath. The heat transfer from the film to the coolant medium is modeled in stages using plane wave theory. The optimum high-frequency response is obtained by matching the acoustic impedance of the multilayered structure to that of the liquid coolant (load). In general, a 20-80% improvement in the transmission coefficient for the generated heat could be gained by the addition of the matching layers.         Electromagnetic radiation mixer based on electron heating in resistive state of superconductive Nb and YBaCuO films    E.M. Gershenzon, G.N. Gol'tsman, Y.P. Gousev, A.I. Elant'ev and A.D. Semenov Summary: A theory of an electron-heating mixer which makes it possible to calculate all the characteristics of the device is developed. It is shown that positive conversion gain is possible for such a mixer in the millimeter to near-infrared wavelength range. The dynamic range and the optimum heterodyne power can be selected from a very wide interval by varying the mixing element volume. Measurements made for Nb within the frequency range of 120-750 GHz confirm the theory. The conversion loss obtained at T=1.6 K and normalized to the element reaches 0.3 dB in the intermediate frequency band of 40 MHz; the possible noise temperature is 50 K. The estimation of noise temperature and output band for YBaCuO at T=77 yields 200 K and more than 10 GHz, respectively.         Mechanism of picosecond response of granular YBaCuO films to electromagnetic radiation    E.M. Gershenzon, G.N. Gol'tsman, A.D. Semenov and A.V. Sergeev Summary: Ultrafast mechanisms of radiation detection in granular YBaCuO films are studied in the wide wavelength range from millimeter waves to near infrared. With an increase in radiation frequency, the Josephson detection at the grain-boundary weak links is replaced by electron heating into the grains. This change occurs in the submillimeter wavelength range. The electron-phonon relaxation time tau /sub eph/ is determined from direct measurements, quasi-stationary electron heating measurements, and the frequency dependence of the current at which maximum voltage shift is observed. The temperature dependence of tau /sub eph/ at T         Influence of surface quality on tunneling and electrical properties of NdCeCuO thin films    A. Kussmaul, J.S. Moodera, P.M. Tedrow, A. Gupta and C.C. Tsuei Summary: Thin films of Nd/sub 1.85/Ce/sub .15/CuO/sub 4-y/ were prepared by laser ablation on heated SrTiO/sub 3/ substrates in 150 mtorr O/sub 2/. After deposition, the films were annealed in vacuum at 820 degrees C. This step is necessary in order to achieve bulk superconductivity in the samples, but it has a deleterious influence on their surface properties. Tunneling characteristics measured on such samples show very broad features, making a determination of the gap very difficult. A very high contact resistance resulted in difficulties with Hall and magnetoresistance measurements. To remedy these problems, the influence of different etches and surface treatments was studied. Specifically, the electrical properties and tunneling characteristics of Au contacts made on acid-etched and ion-milled NdCeCuO thin films were measured. In the case of acetic acid, the current through the contact at low temperatures was shown to be due to tunneling, and the slow temperature dependence makes it likely that this is also the case up to room temperature. For ion-milled surfaces, very similar tunneling characteristics at low temperature were observed, but the temperature dependence suggests a change in the mechanism as the temperature is increased. Gold contacts prepared on acetic-acid-treated surfaces of NdCeCuO thin films have made it possible to measure magnetoresistance and Hall effect from room temperature to 4.2 K, thus solving the initial noise problems encountered.         Proximity effect in the SN interface of high-T/sub c/ superconductors: Tunnel spectroscopy and surface impedance    N. Yoshikawa and M. Sugahara Summary: The authors describe a theoretical investigation of superconducting properties when a thin nonsuperconducting layer exists upon a high-T/sub c/ superconductor surface. The critical temperature, the density of states, the quasi-particle tunneling characteristics, and the surface impedance are calculated, taking into account the proximity effect. The steep order parameter variation in the SN (superconductor-normal metal) interface is shown to cause a large pair breaking perturbation and to affect the surface superconducting properties. It is noted that even the very thin normal layer causes serious degeneration of surface properties in the case of the high-T/sub c/ superconductor because of its short coherence length.         Investigation of ErBa/sub 2/Cu/sub 3/O/sub 7//Cu/sub 2/ O/normal metal tunnel structures    T.P. Thorpe, E.J. Cukauskas, L.H. Allen and M. Reeves Summary: Tunneling studies have been made using sputtered Cu/sub 2/O as an insulating barrier between an EBCO thin film and a normal metallic layer. Cu/sub 2/O was selected for its low potential for chemical reaction with the superconducting layer and for its photoconductive properties. Having a band gap in the visible (2 eV), Cu/sub 2/O is a suitable candidate for photosensitive tunneling experiments. EBCO thin films were deposited in situ onto MgO substrates using an off-axis sputtering technique. T/sub c/'s of as-deposited films were between 80 and 85 K. Inductively measured J/sub c/'s ranged between 10/sup 6/ and 10/sup 7/ A/cm/sup 2/ at 4 K. A 5-20-nm layer of Cu/sub 2/O was sputtered directly on top of the superconducting film. Room-temperature resistivities of the Cu/sub 2/O layer were typically greater than 10/sup 6/ Omega -cm. A normal metal layer (typically gold) was then deposited onto the Cu/sub 2/O layer. Transport properties of the structure were measured at temperatures ranging above and below the T/sub c/ of the superconducting layer. Measurements of structures fabricated to date showed no tunneling effects. Measurements of the I-V characteristic of a Cu/EBCO bilayer exhibited nonohmic behavior at 85 K and 4 K, indicating the existence of an extraneous interfacial layer. Preliminary results on one such structure indicate possible tunneling effects.         YBa/sub 2/Cu/sub 3/O/sub 7- delta //Au/Nb sandwich geometry SNS weak links on c-axis oriented YBa/sub 2/ Cu/sub 3/O/sub 7- delta /    M.C. Foote, B.D. Hunt and L.J. Bajuk Summary: Sandwich geometry superconductor/normal metal/superconductor structures have been fabricated on LaAlO/sub 3/ and cubic zirconia with laser-ablated, c-axis-oriented YBa/sub 2/Cu/sub 3/O/sub 7- delta / base electrodes, 100-600 AA of Au, and Nb counter electrodes, all formed in situ without breaking vacuum. Junctions range in size from 5 to 50 mu m on a side. Four probe I-V measurements at 4.2 K show R/sub n/A products as low as 6*10/sup -9/ Omega cm/sup 2/ and critical current densities up to 5.2 kA/cm/sup 2/. AC Josephson steps were observed with the application of 10-GHz radiation. The temperature dependence of J/sub c/ and the observation of the AC Josephson effect suggest that true supercurrents are present and that they do indeed represent the characteristics of the YBa/sub 2/Cu/sub 3/O/sub 7- delta //Au/Nb structure. The best results were obtained when the devices were annealed at approximately 450 degrees C in O/sub 2/ for 30 min after Au deposition.         Tunneling study of epitaxial YBa/sub 2/Cu/sub 3/O/sub x/ superconducting films    Yu.M. Boguslavsky, E.M. Rudenko and V.M. Mukhortov Summary: Planar and edge-type YBa/sub 2/Cu/sub 3/O/sub x/-metal (Pb, Pt, In) tunnel junctions based on epitaxial Y-Ba-Cu-O films have been studied. The conductance characteristics of these junctions, particularly the conductance zero bias anomalies, have been considered. A difference between the R/sub d/(V) dependences was observed for two types of the contacts at low bias voltages V         Calculation of the Josephson current in p-wave and s-wave superconducting hetero-junctions by Bogoliubov transformation    A. Nakayama and Y. Okabe Summary: A superconducting heterojunction made of a p-wave superconductor and a normal s-wave superconductor is investigated. The Bogoliubov transformation for the p-wave superconductor was obtained by diagonalizing the superconducting Hamiltonian. The value of the Josephson current that flows in the heterojunctions of p-wave/s-wave superconductors was calculated with this Bogoliubov transformation and was shown to be zero in the first-order perturbation at 0 K and at finite temperature. The ground state of the Balian-Werthamer-state superconductor at 0 K was obtained in the second-quantization formalism.         Characteristics of Y-Ba-Cu-O/Nb and Bi-Sr-Ca-Cu-O/Nb tunnel-type Josephson junctions    A. Nakayama, T. Matsui and Y. Okabe Summary: The authors fabricated Y-Ba-Cu-O/Nb and Bi-Sr-Ca-Cu-O/Nb tunnel-type junctions and observed the DC and AC Josephson effects. Gold thin films were deposited for an interlayer to protect the reaction between the base electrode and the tunnel oxide before the tunnel barrier formation. In Y-Ba-Cu-O/Au/MgO/sub x//Nb junctions, superconducting current, hysteresis of current-voltage characteristics, and RF-induced voltage steps as high as 0.13 mV in the current-voltage characteristics were observed. Moreover, the superconducting current was modulated by the magnetic field. In Bi-Sr-Ca-Cu-O/Au/MgO/sub x//Nb junctions, superconducting current and RF-induced voltage steps as high as 0.15 mV were also observed.         YBCO/Pb tunnel junctions: reproducibility, cyclability and role of the oxygen content at the YBCO surface    A.M. Cucolo, R. Di Leo, P. Romano, L.F. Schneemeyer and J.V. Waszczak Summary: Planar tunnel junctions were realized on liquid-etched YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) single crystals with a native barrier and a Pb film as counterelectrode. Reproducibility of the tunneling characteristics has been tested on more than 150 junctions. Cyclability was good for six thermal cycles over the course of 6 mo. The main features on the dV/dI-vs-V curves were gaplike structures at +or-4-5 mV and +or-19 mV and well-defined minima at +or-36 mV. The amplitudes of these structures showed little change when the YBCO single crystals were exposed for 24 h to room atmosphere prior to the Pb evaporation. By heating the samples for 1 h at 400 degrees C in vacuum before the counterelectrode was applied to complete the junction, the structures broadened and shifted toward high energies. For all junctions, subgap leakage currents were less than 5% at 4.2 K, and the Pb gap and phonon structures were clearly shown on the tunneling characteristics, indicating a good-quality tunnel barrier.         Experimental analysis of superconducting properties of Y-Ba-Cu-O/Ag proximity interfaces    A. Fujimaki, Y. Takai and H. Hayakawa Summary: The electrical properties of YBa/sub 2/Cu/sub 3/O/sub 7-y//Ag proximity interfaces are reported. In order to study these properties, SNS (superconductor/normal metal/superconductor) junctions made of YBa/sub 2/Cu/sub 3/O/sub 7-y//Ag/Nb thin films and SNIS (superconductor/normal metal/insulator/superconductor) junctions made of YBa/sub 2/Cu/sub 3/O/sub 7-y//Ag/AlO/sub x//Nb thin films were examined. Experimental results on the SNS junctions imply that weak links are formed inside YBa/sub 2/Cu/sub 3/O/sub 7-y/ and that the junction properties depend on the area of the surface nonsuperconducting phases. The J/sub c/-R/sub n/ relationship and the R/sub n/-T characteristics suggest the presence of nonsuperconducting phases grown partially on the YBa/sub 2/Cu/sub 3/O/sub 7-y/ surfaces. The results on the SNIS junctions show little superconductivity induced in the Ag layers by the YBa/sub 2/Cu/sub 3/O/sub 7-y/ films.         Optimization of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films for multilayers    R.G. Humphreys, N.G. Chew, J.S. Satchell, S.W. Goodyear, J.A. Edwards and S.E. Blenkinsop Summary: The in situ growth of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films has been studied using e-beam coevaporation. The growth conditions for smooth YBa/sub 2/Cu/sub 3/O/sub 7/ films with high T/sub c/ and J/sub c/ have been established. Superconductor-insulator (SI) and superconductor-insulator-superconductor (SIS) structures have been grown using Y/sub 2/O/sub 3/ as an epitaxial insulator, and preliminary vertical transport measurements in patterned structures are reported.         Microscopic observation of interface structures of YBaCuO/MgO/YBaCuO double-heteroepitaxial thin films by TEM    K. Sakuta, M. Iyori, T. Kobayashi, M. Matsui and M. Nakajima Summary: The YBaCuO/MgO/YBaCuO double-heterostructure (DHS) was fabricated using conventional RF magnetron sputtering. The formation of [110]YBaCuO/[100]MgO/[110]YBaCuO on [110]SrTiO/sub 3/ substrate, and [001]YBaCuO/[100]MgO/[100]YBaCuO and [001]YBaCuO/[100]MgO/[001]YBaCuO on [100]MgO substrate are demonstrated. According to RHEED (refraction high-energy electron diffraction) observations, each layer of the DHS was grown epitaxially. The cross-sectional TEM (transmission electron microscope) observation of the [001]YBaCuO/[100]MgO(2 nm)/[001]YBaCuO structure was carried out in order to characterize the heterostructure. The ultrathin MgO layer grew in an island shape. The MgO shape deposited on YBaCuO film is island-like because of the low absorption energy of Mg on the YBaCuO surface and/or large value of MgO/YBaCuO interface free energy. The YBaCuO atomic arrangement shape implied that the YBaCuO growth mechanism was atomic layer epitaxy.         LaAlO/sub 3/-YBCO multilayers    A.E. Lee, J.F. Burch, R.W. Simon, J.A. Luine, R. Hu and S.M. Schwarzbek Summary: The authors describe the growth of HTS (high-temperature superconductor) bilayers (LaAlO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/) and trilayers (YBa/sub 2/Cu/sub 3/O/sub 7//LaAlO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/) using off-axis RF sputtering from single stoichiometric targets. TEM (transmission electron microscope) examination shows that both the LaAlO/sub 3/ and YBa/sub 2/Cu/sub 3/O/sub 7/ films grow epitaxially upon the preceding layer. The interfaces between layers and at the LaAlO/sub 3/ substrates are sharp and clean. It is found that deposition of the subsequent layers does not degrade the electrical properties of the bottom YBa/sub 2/Cu/sub 3/O/sub 7/ layer; this observation extends to the surface resistance and to the superconducting transition temperature of the bottom YBCO layer. The results of the electrical measurements of the multilayer structures made by the off- and on-axis LaAlO/sub 3/ depositions are discussed.         Critical current and relaxation of oriented grained YBa/sub 2/Cu/sub 3/O/sub 7-x/ after fast neutron irradiation    H. Kupfer, C. Keller, R. Meier-Hirmer, K. Salama, V. Selvamanickam and G.P. Tartaglia Summary: The authors investigated the effects of fast neutron irradiation on the superconducting properties of oriented grained YBa/sub 2/Cu/sub 3/O/sub 7-x/ after a fluence of 10/sup 17/ cm/sup -2/. The critical current density J/sub c/ increases up to a factor of 4, reaching 2.7*10/sup 4/ A/cm/sup 2/ when B perpendicular to a,b and 5.3*10/sup 3/ A/cm/sup 2/ when B // a,b, respectively, at 77 K, 2 T. This enhancement is accompanied by a decrease in the activation energy U/sub 0/ in the field and temperature region at which U/sub 0/ passes through a maximum. The unexpected relationship between U/sub 0/ and J/sub c/ points to weak pinning centers introduced by atomic collision or to a change of the electronic structure via oxygen rearrangement. Upon irradiation, the irreversibility field increases slightly in both geometries. The authors also investigated whether intragrain decoupling was introduced and/or increased by irradiation. A simple check from magnetization measurements makes it possible to determine the degree of nonuniform current flow as a precursor of granularity. This investigation indicates no deviation from the nongranular case after irradiation of the current flows within the a,b plane and a tendency towards a more uniform current flow in the other geometry.         Flux pinning and flux creep in uranium-doped (Bi, Pb)-Sr-Ca-Cu-O superconducting powders after thermal-neutron irradiation    H.R. Hart Jr., F.E. Luborsky, R.H. Arendt, R.L. Fleischer, J.E. Tkaczyk and D.A. Orsini Summary: Fission fragment damage was introduced into uranium-doped powdered Bi/sub 1.7/Pb/sub 0.3/Sr/sub 2/Ca/sub 2/Cu/sub 3/ O/sub y/ by irradiation with thermal neutrons. Measurements of magnetic hysteresis and flux creep were made using a vibrating sample magnetometer. Magnetic hysteresis and intragranular critical current densities, obtained from the magnetic hysteresis using the critical state model, show an increase upon irradiation of a factor of 70 at 50 K and 0.8 T. Flux creep data, interpreted as nonlinear relations between pinning energy and magnetization, as temperature-dependent pinning energies, or as distributions of pinning energies, show significant increases in pinning energy upon irradiation. The irreversibility line is found to shift to higher magnetic fields upon irradiation. It is concluded that the increase in flux creep and decrease in critical current density at higher temperatures appear to limit the potential utility of this family of oxide superconductors to the lower-temperature regime.         Calculation of magnetic flux profiles and deduction of critical current densities for type II superconductors    J.R. Cave, P.R. Critchlow, P. Lambert and B. Champagne Summary: The critical state concept for the calculation of internal flux profiles in type II superconductors is used to model the magnetization behavior of high-T/sub c/ materials. In this application of the model, the field-dependent reversible magnetization and critical current density are incorporated flexibly into numerical solutions of the basic equations. The solutions are compared to results obtained by using the Bean (constant J/sub c/) and Kim (field dependent J/sub c/) approximations. The authors use theoretically calculated magnetization curves to analyze experimental magnetization data for bulk, textured Y/ErBaCuO samples obtained from their own work and from recently published work. Pitfalls and guidelines when using such measurements to obtain intrinsic material critical current densities are discussed.         Dissipation in high temperature superconductors in a magnetic field    D.H. Kim, K.E. Gray, R.T. Kampwirth, D.B. McDonald and D.M. McKay Summary: The absence of a Lorentz-force dependence on dissipation in the highly anisotropic high-temperature superconductor Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ has been measured over a wide range of current densities in broadened resistive transitions, current-voltage characteristics, magnetoresistances, and critical current densities, J/sub c/. The magnetoresistances are very useful for determining the correct temperature and field dependences of the activation energy. As an alternative to flux motion, the authors consider a Josephson-coupling model which is consistent with the broadened resistive transitions and the lack of Lorentz-force dependence. It is found that the Josephson-coupling model agrees with the temperature dependences of the activation energy and J/sub c/ and is better matched to the weak-field dependence of J/sub c/ than the flux creep model. Possible origins of Josephson junctions in high-quality films and single crystals are discussed.         Flux creep in superconductors    K.S. Lichtenberger, S.C. Sanders and D.K. Finnemore Summary: Measurements of flux creep have been undertaken for a variety of superconductors' to determine the factors that control the temperature and magnetic field regimes where the material transforms from a strong-pinning rigid-flux lattice material to the region where the flux lattice is highly mobile. Analysis of the data in terms of a single effective pinning potential, U/sub eff/, using the Beasley model indicates that all of the superconductors measured have a gradual transition from the strong pinning behavior at low temperature to weak pinning behavior at high temperature. There is a narrow band of fields and temperatures in the H-T plane where U/sub eff//kT rises from 2 to 100. The position of this band changes considerably from material to material. It is shown that there are some striking similarities and some clear trends in the pinning potentials when they are plotted on a reduced temperature scale. The highly anisotropic Tl-based and Nd-based copper oxides are very similar even though their T/sub c/ values differ by a factor of 5. In the progression from Nb-Ti to the cubic Bi-oxide to the anisotropic Cu-oxide, there is a clear trend to a wider region of high flux creep.         Effects of Ni-doping on the high-magnetic field transport and magnetization properties of single crystals of YBa/sub 2/Cu/sub 3/O/sub 7/    K.A. Delin, T.P. Orlando, E.J. McNiff Jr., S. Foner, R.B. van Dover, L.F. Schneemeyer and J.V. Waszczak Summary: Transport and magnetization measurements are presented for YBa/sub 2/Cu/sub 3-x/Ni/sub x/O/sub 7/ single crystals, where x ranges from 0.0 to 0.03. The presence of nickel systematically sharpens the resistive transition of the material in a high magnetic field, but it does not correlate with the critical current as determined from magnetization measurements. The breadth of the transition for both pure and doped samples, although different, scales according to the model proposed by M. Tinkham Phys. Rev. Lett., (vol.61, p.1658, 1988).         Critical current and magnetic flux noise of YBaCuO thin films in the presence of flux creep    K. Enpuku, T. Kisu, R. Sako, M. Hirata and K. Yoshida Summary: The pinning potential U of YBaCuO films in weak magnetic fields is studied experimentally. It is shown that the pinning potential increases with the increase in the critical current density J/sub c/; values of U(T=0)=25-120 meV are obtained for the films with J/sub c/(T=0)=5.3*10/sup 5/-1.8*10/sup 7/ A/cm/sup 2/. The temperature dependence of the pinning potential U(T) is also obtained. The experimental results can be explained qualitatively by the pinning model of isolated vortices. The properties of the 1/f flux noise of the film are also discussed with the experimental results of the pinning potential. It is shown that the dependences of the flux noise on the temperature and the critical current density can be explained by the properties of the pinning potential.         Critical current properties under high magnetic fields up to 30 T for Y-Ba-Cu-O films by MOCVD    S. Matsuno, F. Uchikawa, K. Yoshizaki, N. Kobayashi, K. Watanabe, Y. Muto and M. Tanaka Summary: Y-Ba-Cu-O superconducting film prepared by MOCVD (metalorganic chemical vapor deposition) was shown to have excellent critical current density of 2.7*10/sup 6/ A/cm/sup 2/ at 77 K, 0 T and 2.5*10/sup 4/ cm/2 at 77 K, 30 T respectively. The upper critical field, B/sub c2/, for the film was estimated to be 59 T at 77 K. The activation energy U/sub 0/(B), of 1.98 eV at 21 T was determined by electrical resistance measurement under magnetic fields. The Cu composition of the film was approximately 75% over from the stoichiometry of YBa/sub 2/Cu/sub 3/O/sub 7-x/ system. The J/sub c/ properties under high magnetic fields strongly depended on the Cu composition of the films. The optimum value of Cu ratio for obtaining the highest J/sub c/ was about 5.2.         Microstructural, transport, and RF properties of multilayer-deposited YBCO films    L. Madhavrao, E.K. Track, R.E. Drake, R. Patt, G.K.G. Hohenwarter and M. Radparvar Summary: Thin films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) have been fabricated by sequential multilayer RF magnetron sputter-deposition from Y/sub 2/O/sub 3/, BaCo/sub 3/, and CuO targets and postannealing in oxygen. This approach readily allows precise control of the film stoichiometry and is promising for applications that require deposition over large areas. Films on different substrates-including SrTiO/sub 3/, LaAlO/sub 3/, MgO and sapphire-are found to be c-axis oriented for film thicknesses between 300 AA and 10000 AA. Transport current densities in the range of 10/sup 6/ A/cm/sup 2/ are obtained on SrTiO/sub 3/ and LaAlO/sub 3/ substrates and in the range of 10/sup 5/ A/cm/sup 2/ on MgO and sapphire. Transition temperatures of 89 K (resistive) and 87 K (inductive) are obtained repeatably with LaAlO/sub 3/ substrates. Copper cavity end wall measurements at 77 K and 35.6 GHz set an upper limit for the surface resistance of the YBCO films on LaAlO/sub 3/ that is equal to the surface resistance of high-quality silver films. The fabrication and properties of these films are discussed.         Preparation of thin films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ by magnetron sputtering techniques    L.H. Allen, E.J. Cukauskas, P.R. Broussard and P.K. Van Damme Summary: Three variations of sputtering for growing thin films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ are examined: a three-metal cosputtering technique requiring a postanneal at high temperatures, an in situ process using a inverted cylindrical magnetron sputter gun, and another in situ process using an planar target in an off-axis geometry. The films are grown primarily on a magnesium oxide substrate because it is readily available, inexpensive, and its low dielectric constant permits convenient microwave circuit design. It is found that the cosputter process with postanneal produces films with depressed T/sub c/'s and J/sub c/'s. The inverted cylindrical magnetron sputtering has yielded the best films, showing complete transitions as high as 87 K and J/sub c/=4*10/sup 6/ A/cm/sup 2/ at 4 K. The off-axis results are not quite as good, with 79 K complete transitions. By lowering the substrates further out of the plasma in the off-axis system, films can be improved by avoiding damage from negative ions.         Growth of C-axis oriented YBaCuO films on oxidized textured Ni sheets and on    A. Ginsbach, R. Schneider, H.W. Grueninger and G. Grabe Summary: YBaCuO films were grown on oxidized textured Ni sheets and on (100)- and (110)-oriented NiO single crystals by magnetron sputter deposition from a stoichiometric tubular target. The properties of the YBaCuO films are investigated as a function of various preparation parameters (oxidation procedure of the sheets, substrate temperature T/sub s/, and superconductor film thickness). At T/sub s/=780 degrees C and for film thickness larger than 200 nm, the films have T/sub c/ values around 80 K. The textures of the Ni sheets, NiO layers, and YBaCuO films are determined by using X-ray diffraction in Bragg-Brentano geometry and scanning electron microscopy. It is shown that on textured oxidized Ni the YBaCuO films grow c-axis oriented. For comparison, the properties of films on differently oriented NiO single crystals are investigated. It is found that the film properties are better on (100) than on (110) surfaces.         Highly reliable epitaxial YBaCuO thin-films using pressure-controlled magnetron sputtering method    K. Sakuta, M. Iyori, T. Awaji and T. Kobayashi Summary: The authors systematically investigated the effects of discharge gas pressure on in situ YBaCuO thin-film formation by RF magnetron sputtering and ensured the reliability of the epitaxial YBaCuO films by pressure control. The film (100-nm thick and no protection) showed no sign of degradation in its T/sub c/ value for approximately 3000 h. Under the controlled discharge gas pressure, the in situ epitaxial YBaCuO film had a T/sub c/ of 87 K. The c-axis lattice constants and the critical temperatures came very close to the bulk values as the pressure was rising to 1 torr. The plasma emission spectra showed a reduction in the Ar spectrum intensities relative to the oxygen component with increasing pressure. This observation suggests that the reduced mean free path of the gas atoms is responsible for the improved film crystallinity and superconductivity.         Processing and yield of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ thin films and devices produced with a BaF/sub 2/ process    D.B. Laubacher, D.W. Face, R.J. Small, C. Wilker, A.L. Matthews, I. Raistrick, F.H. Garzon, J.G. Berry, P. Merchant, J. Amano and R.C. Taber Summary: High-quality films were produced by coevaporation and cosputtering of Y, Cu, and BaF/sub 2/ followed by an ex-situ anneal. The Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ films produced had microwave surface resistances as low as 1/10 that of Cu at 77 K and 10 GHz. This process is especially useful for producing uniform films over areas larger than 1 in/sup 2/ and is compatible with lift-off or traditional etch patterning processes for fabrication of microwave devices. More than 100 films have been deposited on (100) LaAlO/sub 3/ with various compositions and anneal conditions. Films were characterized by a wide variety of techniques aimed at optimization of film quality through process control. Emphasis was placed on determining the relationship between material properties and film microwave performance. Run-to-run reproducibility for a sample set of over 20 films was determined. In addition, C-band 5-GHz microstrip resonators were fabricated from these microwave-characterized films. Unloaded Q's of these devices have exceeded 7500 at 77 K, compared to normal metal resonator Q's of 300 for this structure. These Q's correlate well with predicted performance based upon the previously measured microwave surface resistance of the unpatterned films.         In-situ crystallization of YBaCuO films by the RF-diode sputtering method    H. Kajikawa, Y. Fukumoto, S. Hayashi, K. Shibutani, R. Ogawa and Y. Kawate Summary: A recently developed temple-bell-type substrate holder in the conventional RF-diode sputtering method was used to obtain high-quality YBa/sub 2/Cu/sub 3/O/sub 7-y/ films. Avoiding the rush of negative ions into the films by placing the substrate perpendicular to the target surface led to the formation of highly oriented films with smooth surfaces on the various kinds of oxide substrates. The as-grown films deposited on SrTiO/sub 3/ [100], SrTiO/sub 3/[110], and MgO [100] substrates showed a transition temperature of >80 K. The critical current densities were improved by post-oxygen annealing and reached values of more than 2*10/sup 5/ A/cm/sup 2/ at 77 K in the films on the MgO [100] and SrTiO/sub 3/ [100] substrates. However, AC susceptibility measurement showed that many weak links, presumably due to oxygen deficiencies, remained.         Characteristics of high T/sub c/ superconducting thin films prepared by chemical vapor deposition    S. Aoki, T. Yamaguchi, N. Sadakata and O. Kohno Summary: Superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films were prepared at 750-840 degrees C by chemical vapor deposition (CVD) using beta-diketonate chelates on single-crystal SrTiO/sub 3/, MgO substrates, and metal substrates. The best films on single-crystal MgO had zero-resistance T/sub c/ at 89 K and J/sub c/ above 3.6*10/sup 4/ A/cm/sup 2/ (at 77.3 K, 0 T). On SrTiO/sub 3/, the best films had T/sub c/ at 92.5 K and J/sub c/ above 2.0*10/sup 5/ A/cm/sup 2/. X-ray diffraction confirmed the existence of orthorhombic crystal structures having c-axis orientation. The magnetic field dependence of J/sub c/ of the YBCO film was measured at 77.3 K. J/sub c/ depends on the angle between the direction of the applied field and that of the c-axis of YBCO. Superconducting tapes that are 10-cm long were obtained by CVD using Ni-based alloy as a substrate. These tapes had the crystal structures of YBa/sub 2/Cu/sub 3/O/sub 7-x/ [110]-oriented and T/sub c/ at 84.5 K. The strain dependence of J/sub c/ was measured. Bending strain of up to 0.08% did not reduce J/sub c/.         The behaviour and properties of in-situ formed YBa/sub 2/Cu/sub 3/O/sub x/ thin films during reversible oxidation/deoxidation    G.W. Morris, E.J. Tomlinson, R.E. Somekh, Z.H. Barber, E.J. Williams, M.P. Ray and J.E. Evetts Summary: The authors have reversibly oxygenated and deoxygenated in situ-formed thin films of YBa/sub 2/Cu/sub 3/O/sub x/ by means of low-temperature anneals in oxygen and argon. The transition shape for slightly deoxygenated material is consistent with the existence of two superconducting phases, which may be distinguished by different oxygen ordering. The authors investigated J/sub c/(B) as a function of oxygen content in samples whose oxygen content has been controlled by low-temperature anneals. The steep rise in J/sub c/ with T/sub c/. has been demonstrated and the effect on J/sub c/ of change in c investigated. It is confirmed that in situ-formed films which have low T/sub c/ as-deposited have anomalously high c values, but it is demonstrated that good films (that is, films which as deposited have c approximately 1.168 nm and T/sub c/ approximately 90 K) follow the bulk c vs. T/sub c/ relationship when deoxygenated and reoxygenated in low-temperature anneals. The cause of the c expansion is attributed to a defect, possibly the substitution of Ba for Y, introduced at the time of film deposition under conditions of low mobility. Some data have been obtained which suggest that films deposited on substrates at higher temperatures have c vs. T/sub c/ more consistent with bulk data.         The processing and properties of high T/sub c/ thick films    T.W. Button, N.M. Alford, F. Wellhofer, T.C. Shields, J.S. Abell and M. Day Summary: The influence of processing conditions on the microstructure and properties of YBa/sub 2/Cu/sub 3/O/sub x/ thick films on yttria-stabilized zirconia substrates is reported. Films processed below the peritectic temperature are fine grained, exhibit little preferred orientation, and generally have low critical currents. Above the peritectic temperature, the morphology changes dramatically and large, highly textured, spherulitic crystals are observed, with an associated increase in critical current and an improved T/sub c/. Properties in these materials are generally much better than those of bulk YBa/sub 2/Cu/sub 3/O/sub x/ . The relationship between microstructure and properties is shown to be complex. The influence of silver additions to the films is examined, and examples are given of thick-film devices which are being evaluated. Thick-film devices under evaluation include flux transformers, TE/sub 011/ cavities, coaxial and helical resonators, microstrip resonators, current limiters, and shields.         Electrophoretic deposition of Bi-based superconductors with T/sub c/ near 80 K    J.C. Ho, H.B. Liu, C.Y. Wu, P.G. Wahlbeck, D.L. Myers, S. He and F.J. Schmidt Summary: The feasibility of electrophoretically depositing the 2212 phase of BSCCO onto silver substrates has been established. By choosing suitable processing parameters, the resulting thick films have smooth surfaces without cracks and exhibit well-defined superconducting transitions near 80 K. Results on the temperature dependence of the electrical resistance of deposited Bi-Sr-Ca-Cu-O and Bi(Pb)-Sr-Ca-Cu-O films with different sintering conditions are presented.         Selective epitaxial growth of YBaCuO thin films and its application to MOSFET fabrication    S. Hashiguchi, E. Min, T. Awaji, K. Asano, U. Kabasawa, K. Sakuta and T. Kobayashi Summary: The feasibility of selective (001)-Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/ epitaxy is examined. The selective growth of epitaxial Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/ and heteroepitaxial (100)-MgO/(001)-Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/ layers through the SiO window was obtained. For defining the epitaxial growth region, the partial coating of the MgO substrate with the reactive SiO was used. The Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/ deposited through the SiO window grew epitaxially; the film formed directly on the SiO layer was semitransparent, electrically insulating, and amorphous. MOS capacitors and MOSFETs were fabricated in the same way.         Properties of superconducting YBa/sub 2/Cu/sub 3/O/sub 7- delta/ time films made at high deposition rates    X.D. Wu, R.E. Muenchausen, S.R. Foltyn, R.C. Estler, N.S. Nogar, A.D. Rollett, C.C. Chang, P. England, R. Ramesh, D.M. Hwang and T.S. Ravi Summary: High T/sub c/ and J/sub c/ YBa/sub 2/Cu/sub 3/O/sub 7- delta /, thin films were prepared by pulsed laser deposition using deposition rates up to 145 AA/s. It is demonstrated that the deposition rate is one of the important processing parameters for preparation of high-temperature superconducting thin films. At high deposition rates, outgrowths were found on the film surfaces as a result of island growth at the processing temperature needed for good film growth. It is concluded that smooth films can be deposited by choosing the right deposition temperature and deposition rate so that the film coalesces at the final thickness.         Bias effect on the preparation of YBa/sub 2/Cu/sub 3/O/sub 7- delta / films by laser ablation    H. Izumi, K. Ohata, T. Morishita and S. Tanaka Summary: Bias effects on the preparation of superconducting thin films by pulsed laser deposition have been investigated by means of time-of-flight mass spectroscopy. Since a large number of electrons were emitted from the target at the same time as ions during ablation, ions in the plume are shielded from the external electric field by electrons and are not influenced by substrate biasing. Under positively biased conditions, the electron emission was greatly enhanced. Multivalenced ions (Cu/sup 2+/ and Cu/sup 3+/) were also observed in these conditions. It can be understood qualitatively that the rapid extraction of electrons from the target surface by the electric field tends to generate the multivalenced ions. It was also found that the multivalenced ions have an energy of more than 250 eV, which is higher than that of the other atomic ions. Energy differences between the atomic and molecular ions have been observed. While the former have energies of about 200 eV, the latter have energies of a few tens of electronvolt. This indicates that the atomic ions are accelerated in the initial laser ablation process and that the molecular ions are produced in the plasma reactions in the plume. Cluster ions of the mass number of several hundreds were also observed and also had energies of a few electronvolts. It was also found that the laser plume of the YBa/sub 2/Cu/sub 3/O/sub 7- delta /, target is poor in the CuO/sup +/ ion compared to the plasma of other metals.         Active HF and microwave noise spectroscopy for characterization of superconducting materials    J. Konopka and G. Jung Summary: Most superconducting materials under a suitable DC current bias emanate excess noise which may extend from low frequencies up to the terahertz region. The microwave noise in some granular high-T/sub c/ films at 12 GHz can be as high as 10 pW in a 100-MHz bandwidth. The authors studied this noise in Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O thin films grown on different substrates in the temperature range from 4.2 to 100 K in the frequency bands 0-2 GHz and 11-12.5 GHz, using current bias and magnetic field as experimental variables. Analysis of the measurements provides valuable information on the superconductor crystalline microstructure, the parameters of the intrinsic Josephson clusters, the synchronization of the radiation from clusters, and the properties of the intergranular inclusions. In particular, the degree of granularity, the strength of the pinning centers, and the size and the geometry of weak links and of weak-link clusters can be deduced from the noise amplitude and frequency dependence measured as a function of the bias current and externally applied magnetic field. Noise emission tests can be easily performed along with standard superconducting transition measurements, providing instant microstructural information without the need for a sophisticated electron microscope.         In-situ fabrication of Y-Ba-Cu-oxide thin films by pulsed laser deposition    R.M. Bowman, A.I. Ferguson and C.M. Pegrum Summary: The authors report the in situ deposition of laser-ablated YBa/sub 2/Cu/sub 3/O/sub 7- delta / films on MgO substrates, using the third and second harmonics of an Nd-YAG laser. The conditions needed during postdeposition oxygenation to produce the best films were investigated. Highly oriented samples were made using the third harmonic (wavelength lambda =355 nm) on <100> MgO and have a transition temperature T/sub c/ of 85 K and a critical current density J/sub c/ of 1.5*10/sup 5/ A/cm/sup 2/ at 77 K, which rises to 9*10/sup 6/ A/cm/sup 2/ at 4.2 K. Films made with the second harmonic on MgO are, as expected, markedly poorer in quality. Highly oriented films have also been made on <110> and <100> SrTiO/sub 3/ with lambda =355 nm. Deposition on SrTiO/sub 3/ has yielded lower T/sub c/'s, probably due to poor-quality substrates. Anisotropic resistivity in films on <110> SrTiO/sub 3/ has been observed, with superconducting transitions in both directions.         Properties of ion-beam deposited YBCO thin films    K. Li and J.E. Johnson Summary: YBCO thin films have been fabricated by single-target ion-beam deposition methods on MgO and LaAlO/sub 3/ substrates. The best T/sub c/ for YBCO on MgO substrates by the 900 degrees C ex-situ post-annealing process was found to be 80 K. It is believed that the presence of one or more nonsuperconducting phases in the conduction path led to the degradation of T/sub c/ values to levels below those expected for the bulk crystalline material. The best T/sub c/ for YBCO deposited on an LaAlO/sub 3/ substrate, by the in situ process with molecular oxygen and at a substrate temperature of 750 degrees C, was found to be 83 K. The best T/sub c/ using the atomic oxygen process was 80 K. The degradation of these T/sub c/ values below those of the bulk crystalline material is explained by the expansion of c-lattice parameters. The properties of these films were studied through microscopy, stoichiometry, X-ray diffraction, Auger analysis, and T/sub c/ measurements.         High quality flux control system for electron gun evaporation    H.M. Appelboom, P. Hadley, D. van der Marel and J.E. Mooij Summary: A high-quality flux control system for electron gun evaporation has been developed and tested for the MBE (molecular beam epitaxy) growth of high-temperature superconductors. The system can be applied to any electron gun without altering the gun itself. Essential elements of the system are a high-bandwidth mass spectrometer, control electronics, and a high-voltage modulator to sweep the electron beam over the melt at high frequencies. The sweep amplitude of the electron beam is used to control the evaporation flux at high frequencies. The feedback loop of the system has a bandwidth of over 100 Hz, which makes it possible to grow superlattices and layered structures in a fast and precisely controlled manner. The drift of the total system is dominated by the temperature drift of the secondary emission multiplier in the mass spectrometer. This drift is typically 1-2%/h for copper as measured by an independent quartz-crystal thickness monitor. The system has been successfully tested with evaporation rates of 0.001 to 1 nm/s for various materials and under ozone and oxygen pressures up to 10/sup -4/ mbar. The feedback system has successfully been used for the fabrication of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films.         Critical current behavior of Ag-coated YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films    R.H. Ono, J.A. Beall, T.E. Harvey, C.D. Reintsema, M. Johansson, M.W. Cromar, L.F. Goodrich, J. Moreland, A. Roshko and T.C. Stauffer Summary: The authors studied the behavior of high-quality Ba/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films with Ag overlayers. The authors chose to study Ag in detail because of its widespread use as contact metallization and because of their earlier studies of proximity effects in YBCO. The details of transport critical current measurements are presented. It is shown that the Ag coatings can reduce normal state resistance while not degrading the critical current density. The key technological result is that the various thicknesses of Ag that were used did not reduce J/sub c/ or J/sub c/(H). Critical current densities in excess of 10/sup 6/ A/cm/sup 2/ have been achieved at temperatures greater than 76 K. An unusual effect was seen in J/sub c/(H) when the field was oriented perpendicular to the c axis of the film. The J/sub c/ at 1 T was higher in samples with 10-nm coatings of Ag than in similar uncoated samples. It was also shown that the composite resistance of Ag-YBCO bilayers can be much lower than the resistance of uncoated YBCO.         The 'in-situ' preparation and properties of Y-Ba-Cu-O thin films on the SrTiO/sub 3/, Al/sub 2/O/sub 3/ and Si substrates    M.I. Faley, M.E. Gershenson, N.P. Kuchta and V.S. Salun Summary: YBa/sub 2/Cu/sub 3/O/sub x/ thin (d=0.1-1 mu m) films were prepared in situ on single-crystal SrTiO/sub 3/ (100), sapphire, and Si heated substrates by RF magnetron sputtering from sintered targets. The spatial distribution of the film contents in the substrate holder plane was measured. Films with stoichiometric composition and mirrorlike surfaces were fabricated. High critical parameters of the films were achieved. Crystal structure, resistivity, and critical current were studied along with the film surface degradation because of the storage in air. The proximity tunnel structure YBCO/Ag/Al/Al-oxide/AI was fabricated, and the gap structure was observed up to T/sub c/ of the YBCO film.         Melt processing of bulk high T/sub c/ superconductors and their application    M. Murakami, T. Oyama, H. Fujimoto, S. Gotoh, K. Yamaguchi, Y. Shiohara, N. Koshizuaka and S. Tanaka Summary: The authors report a melt-powder-melt-growth (MPMG) process which results in high J/sub c/ for bulk Y-Ba-Cu-O superconductors. The Y-Ba-Cu-O pellets or powders are melt quenched. The quenched plates are crushed into powder and mixed well. The powder is then compacted into desired shapes, remelted, and slowly cooled in a thermal gradient. When the starting composition is changed from the 1:2:3 stoichiometry toward the Y/sub 2/BaCuO/sub 5/ (211) rich region, the 211 inclusions can be dispersed in the YBa/sub 2/Cu/sub 3/O/sub x/ matrix, which contributes to increases in both flux pinning force and fracture toughness. A J/sub c/ value exceeding 3*10/sup 8/ A/m/sup 2/ has been achieved at 77 K and 1 T. Another attractive feature of the MPMG process is that other components such as fine Ag powders can be added during solid-state mixing. Fine dispersion of Ag particles can effectively reduce the amount of cracking. MPMG-processed Y-Ba-Cu-O with Ag doping can levitate a mass of 3-kg at 1-mm height using a repulsive force against a 0.4-T magnet. A noncontacting rotation device such as a magnetic bearing can be made utilizing bulk high-J/sub c/ materials. A superconducting permanent magnet is also a promising candidate for future application. MPMG-processed Y-Ba-Cu-O can generate 0.25 T at 77 K.         Rapid solidification of high-T/sub c/ oxide superconductors by a laser zone melting method    S. Nagaya, M. Miyajima, I. Hirabayashi, Y. Shiohara and S. Tanaka Summary: The direct crystallization of the YBa/sub 2/Cu/sub 3/O/sub 7/ orthorhombic superconducting phase from the solution of the 123 composition has been realized by a rapid solidification using a laser zone melting method. This method is characterized by two processing parameters: the temperature gradient (G) and the growth rate (R). Under the higher G and R conditions, the nonequilibrium phase transformation occurred, and the direct crystallization of the orthorhombic phase from the melt of the 123 composition was realized. An as-grown solidification sample exhibited superconducting phase transition at 94 K, according to a magnetization measurement. The structure in which Y/sub 2/O/sub 3/ fine particles dispersed homogeneously was obtained in the lower R region. It is possible to use this structure as a long and narrow precursor for the melt process. By annealing at 1000 degrees C, the critical current density of the sample was 1.5*10/sup 4/ A/cm/sup 2/ at 77 K, 0 T, according to a magnetization measurement.         Phase formation and melt textured growth of (Bi,Pb)-Sr-Ca-Cu-O    Y. Yamada, T. Graf, E. Seibt and R. Flukiger Summary: A textured structure of (2223) phase in the (Bi,Pb)-Sr-Ca-Cu-O system with grain sizes >or=200 mu m was successfully obtained by melt-textured growth using Ag-sheathed tapes and a reduced-oxygen atmosphere. The (2223) phase occupied more than 80% in volume fraction and was oriented within the a-b plane parallel to the tape flat surface. This high-volume friction was achieved by suppressing the Ca/sub 2/CuO/sub 3/ segregation which prevents homogeneous reaction. Melting, rapid cooling, and slow cooling in the present process were found to have a crucial effect on the complete mixing of the elements, suppressing the intermediate precipitates and promoting the crystal orientation, respectively. Consequently, this resulted in the oriented (2223) phase with grain sizes up to several hundred microns.         Grain alignment and transport properties of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8 /grown by laser-heated float zone method    J. Luo, X.P. Jiang, H.M. Chow, M.J. Cima, J.M. Graybeal, T.P. Orlando and D.A. Rudman Summary: A single-phase Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ bulk superconductor (T/sub c/ approximately=82 K) has been grown by the laser-heated float zone method. The samples are highly textured with the grains. typically 100 mu m diameter and 0.5-cm long, and elongated along the crystal a-axis. which is the preferred growth direction. X-ray analysis and transport measurements indicate that all three principal axes (a, b, c) are oriented from grain to grain. The upper limit of the misalignment between the grains is estimated to be less than 2 degrees from the measured anisotropy ratio. The critical current density for such highly textured polycrystalline samples is anisotropic and limited mainly by the weak links at the grain boundaries. The grain boundary effects are examined on the basis of the measured temperature and magnetic field dependence of the critical current.         Magnetisation measurements on melt-textured YBa/sub 2/Cu/sub 3/O/sub 7- delta /    J.R. Laverty, Z.X. Shen, N.M. Alford, T.W. Button, A.D. Caplin, S.M. Cassidy, D.G. McCartney and R.J. Pollard Summary: Quasi-single-crystal specimens were grown from rods of bulk YBa/sub 2/Cu/sub 3/O/sub 7- delta / by a-melt-textured (MT) growth process. The material's magnetization was highly anisotropic, which supports the microstructural picture. While M-H data show that there is a high bulk critical current density, the flux creep behavior indicates that pinning in MT material differs little from that in single crystals or grains of sintered material. The anomalous magnetization reported by M. Daeumling et al. (1990) was observed in only one of three samples taken from the same rod.         AC and DC transport current in melt-grown YBCO    Z. Yi, S. Ashworth, C. Beduz and R.G. Scurlock Summary: It has been suggested that the transport J/sub c/ in multigrain samples of bulk YBCO is limited by the intergrain links. The authors report on preliminary measurements of intergrain currents. The intergrain critical currents in melt-grown YBCO do not appear to be as sensitive to the precise crystallographic alignment of adjacent grains as has been reported for thin films. The measured critical current of similar grain boundaries varies widely, between 15000 A/cm/sup 2/ and 200 A/cm/sup 2/ for adjacent boundaries in the same sample. Preliminary results support the conclusions of S.E. Babcock et al. (Nature, vol.347, p.167, 1990), who found weak-link-free behavior in some high-angle boundaries between bulk crystals.         Surface resistance of bulk and thick film YBa/sub 2/Cu/sub 3/O/sub x//ss    N.M. Alford, T.W. Button, G.E. Peterson, P.A. Smith, L.E. Davis, S.J. Penn, M.J. Lancaster, Z. Wu and J.C. Gallop Summary: The surface resistance R/sub s/ of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) has been measured by means of a coaxial method using a copper outer shield and an HTS (high-temperature superconductor) central conductor as well as by means of an all-YBCO TE/sub 011/, cavity. The microstructure of the ceramic deliberately altered so that variables such as starting powder size and phase purity, ceramic density, phase composition, grain size, and number of grain boundaries can be evaluated. A number of experiments have been conducted so that the variables chosen might be studied independently. The results show that R/sub s/ varies in a complex manner according to the microstructure and that as sintered grain size is reduced to a certain size the R/sub s /is reduced. Further decreases in grain size are associated with an increase in the number of grain boundaries and an increase in the R/sub s/, suggesting that grain boundary detritus and grain boundaries themselves are sources of loss. The R/sub s/ is also highly dependent oil crystallographic orientation, and examples are given to show that R/sub s/ diminishes in c-axis-oriented YBCO thick films.         Superconducting, transition, and normal state photoresponse in YBCO observed at different temperatures    N. Bluzer, D.K. Fork, T.H. Geballe, M.R. Beasley, M.Y. Reizer, S.R. Greenfield, J.J. Stankus and M. Fayer Summary: The photoresponse of YBCO films was measured with a novel technique between 7 K and 200 K. YBCO was exposed to variable-fluence (         Photoresponse of Nb films; observation of biexponential recovery times of the superconducting state    M. Johnson, N. Bluzer, M. Reyzer, T.H. Geballe, S.R. Greenfield, J.J. Stankus, M.D. Fayer and C. Herring Summary: The authors present a systematic study of the photoresponse of superconducting Nb films over ranges of fluence and bias current and for temperatures of 6.5 K         10 GHz surface impedance measurements of (Y,Er)BaCuO films produced by MOCVD, laser ablation, and sputtering    J. Luine, K. Daly, R. Hu, A. Kain, A. Lee, H. Manasevit, C. Pettiette-Hall, R. Simon, D. St. John and M. Wagner Summary: A parallel-plate resonator technique previously used to measure microwave surface resistance R/sub s/(T) has been extended to measure absolute penetration depth lambda (T). Measurements of both quantities near 10 GHz from 4.2 K to T/sub c/ are reported for ErBaCuO thin films produced by metalorganic chemical vapor deposition (MOCVD) and for YBaCuO thin films produced by laser ablation and single-target off-axis sputtering. Each production method gives rise to films whose surface resistance is below 1 m Omega at temperatures below 40 K. The low-temperature penetration depths range from 250 nm for the laser ablation and sputtered films to 800 nm for the MOCVD films. The penetration depths in all cases increase with temperature according to the Gorter-Casimir temperature dependence.         Measurements of the RF surface resistance of high-T/sub c/ superconductors    J.R. Delayen, C.L. Bohn and C.T. Roche Summary: An experimental program is being conducted to assess the applicability of high-T/sub c/ superconductors for use in high-power RF and microwave devices. The program involves the measurement of the RF surface resistance of high-T/sub c/ samples at frequencies between 0.15 and 40 GHz and RF surface magnetic fields as high as 640 G. Polycrystalline samples were found to have surface resistances which increase monotonically with RF-field amplitude, saturating at high field at a few percent of the normal-state surface resistance just above T/sub c/. The data indicate that for high-T/sub c/ materials at low-RF fields, sufficiently low surface resistances are achieved, but at high fields (e.g. >or=30 G) the surface resistances are too large by a factor typically approximately 100.         Detection of light using high temperature superconducting microstrip lines    J.C. Culbertson, H.S. Newman, U. Strom, J.M. Pond, D.B. Chrisey, J.S. Horwitz and S.A. Wolf Summary: The authors report the results of measurements of the effects of external light on the transmission of microwaves through superconducting YBa/sub 2/Cu/sub 3/O/sub 7- delta / microstrip lines. The microstrip geometries used include an asymmetric ring and a meander path. Measurements were made as a function of the microwave frequency (up to 12 GHz), temperature (above to below the superconducting transition temperature), and microwave power. The authors variations in the T/sub c/ of the superconductor, caused by locally varying microwave current densities (standing-wave component). At low microwave powers, this technique can be used to optically probe the local character of the superconducting film without having to move contacts over the film. The asymmetric ring microstrip interferometer was observed to show light-induced shifts in the null frequencies due to the kinetic inductance effect.         Nonbolometric infrared detection in thin superconducting films via photoproduction of fluxon pairs    A.M. Kadin, M. Leung, A.D. Smith and J.M. Murduck Summary: Conventional models have been unable to account for observations of enhanced infrared photodetection in granular superconducting films. The authors propose a mechanism for quantum-limited photodetection in thin films of either conventional or high-temperature superconductors. A photon with hf>>2 Delta is absorbed at a spot in the film, creating a pair of highly excited quasi-particles which very rapidly break additional Cooper pairs and distribute the excess energy among a large number of quasi-particles. This mechanism is essentially a photon-assisted phase slip, in which the photon supplies the additional energy needed to permit the current to nucleate the vortex pair. Assuming unity quantum efficiency for this process, the time-average voltage responsivity is Phi /sub 0//hf=1/(2ef), which yields 10/sup 4/ V/W for 1-eV photons. This picture of photofluxonic detection in a superconductor is directly analogous to photoconductive detection in an intrinsic semiconductor via photoproduction of electron-hole pairs. Experimental evidence of nonbolometric photodetection in an NbN thin film is presented and critically examined in light of this mechanism. The application of devices based on this principle for fast, sensitive infrared detectors is discussed.         UV-light irradiation effects on oxide superconducting thin films    A. Enokihara, S. Kohiki, H. Higashino, K. Setsune and K. Wasa Summary: Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ thin films prepared on (100) MgO substrates by RF magnetron sputtering were irradiated with ultraviolet (UV) light in He gas of about 500 Pa using a low-pressure mercury lamp. The zero-resistance temperature and the critical current density were gradually decreased with irradiation time. X-ray photoemission spectra showed that the mean Cu valence of the film was decreased approximately from +2 to +1 by the irradiation, while the valence of Bi ions was not changed. These results imply that the UV irradiation selectively reduces Cu ions and that the superconductivity strongly depends on the Cu valence.         Femtosecond dynamics of quasi-particles in YBa/sub 2/Cu/sub 3/O/sub 7- delta / superconductor films    S.G. Han, Z.V. Vardeny, O.G. Symko and G. Koren Summary: The transient electronic response of epitaxially grown YBa/sub 2/Cu/sub 3/O/sub 7- delta / superconductor thin films in the femtosecond time domain was investigated using transient photoinduced reflectivity ( Delta R) with 60-fs time resolution. For temperatures T>T/sub c/, only a bolometric signal was observed with Delta R>0. For T0. The results for T         In-situ deposition and processing of YBa/sub 2/Cu/sub 3/O/sub 7-x/ films and multilayers for optoelectronic devices    J.C. Villegier, H. Moriceau, H. Boucher, R. Chicault, L. Di Cioccio, A. Jager, M. Schwerdtfeger, M. Vabre and C. Villard Summary: In situ direct deposition at approximately 700 degrees C of thin YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconductive films and multilayers has been done by three techniques using stoichiometric YBa/sub 2/Cu/sub 3/O/sub 7-x/ sintered targets. Excimer laser ablation in a DC magnetron system with hollow and planar targets leads to 0.5-, 1.2-, and 2.5-in diameter uniformly superconductive layers under static conditions. High critical current densities (>10/sup 6/ A cm/sup 2/ at 77 K) associated with low resistivity and good epitaxial behavior are achieved on top of MgO, SrTiO/sub 3/, LaAlO/sub 3/, and YSZ single-crystal wafers. High-quality c-oriented films (T/sub c/>80 K) are routinely obtained by means of a DC magnetron on large sapphire (>2 in) substrates covered by a YSZ RF sputtered buffer layer. The infrared properties of such films have been checked at 1.15- mu m wavelength. In order to achieve active devices (such as optical detectors and high-frequency mixers), small (<10- mu m/sup 2/) YBa/sub 2/Cu/sub 3/O/sub 7/-YSZ-Ag tunnel junctions and arrays have been successfully patterned in the superconductor/insulator/normal-metal trilayers using SNOP (selective niobium overlap process).         Femtosecond thermomodulation studies of low and high-T/sub c/ superconductors    D.W. Face, S.D. Brorson, A. Kazeroonian, J.S. Moodera, T.K. Cheng, G.L. Doll, M.S. Dresselhaus, G. Dresselhaus, E.P. Ippen, T. Venkatesan, X.D. Wu and A. Inam Summary: The authors report femtosecond pump-probe measurements of electronic energy relaxation in conventional metallic and high-T/sub c/ oxide superconductors. In conventional metallic superconductors, the energy relaxation rate of electrons is used to determine the electron-phonon coupling constant lambda . The agreement between the lambda values measured and those obtained by other techniques is excellent, confirming the theoretical predictions of P.B. Allen (1987). A novel Cu overlayer technique was developed in order to measure certain metals which do not have a strong optical transition to states near the Fermi level at a laser energy, of 1.98 eV. The effect of different Cu overlayer thicknesses has been studied. In the new copper-oxide high-T/sub c/ superconducting materials, electronic energy relaxation is monitored by measuring changes epsilon /sub 2/. The observed changes in epsilon /sub 2/ are related to the dynamics of the Cu d to O p band charge transfer excitation occurring in the CuO/sub 2/ planes. By depleting a YBa/sub 2/Cu/sub 3/O/sub 7- delta / sample of oxygen, one can simultaneously vary the Fermi level and the T/sub c/ and make dramatic changes in the pump-probe signal. An estimate of lambda , in several high-T/sub c/ materials, is also made using Allen's theory to fit the relaxation behavior of epsilon /sub 2/.         In-situ preparation of superconducting Bi-Sr-Ca-Cu-O thin films by high pressure DC sputtering    R.J. Lin and P.T. Wu Summary: Superconducting Bi-Sr-Ca-Cu-O films on (100) MgO substrates have been reproducibly prepared by the high-pressure DC sputtering process without further annealing treatment. The sputtering gas was Ar-50%O/sub 2/, and total gas pressure was 1.5 torr. The target was Bi/sub 2/Sr/sub 2/Ca/sub 1.3/Cu/sub 2/O/sub x/ composite made by solid-state reaction. The substrate temperatures were 600-750 degrees C. The film thickness is 0.8-1.5 mu m. The films consisted of highly c-oriented Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ or Bi/sub 2/Sr/sub 2/Cu/sub 1/O/sub x/ phase. The best superconducting properties of the films are T/sub c/(onset)=93 K and T/sub c/ (R=0)=68 K. The detailed process and effect of processing parameters on superconductivities, phases, and surface morphologies of the films are discussed.         Effect of Tl-sources on growth of Tl-Ba-Ca-Cu-O films by diffusion process    R.J. Lin, D.H. Kuo and P.T. Wu Summary: Superconducting Tl-Ba-Ca-Cu-O films on (100) MgO substrates have been reproducibly prepared by wrapping Ba/sub 1/Ca/sub 2.5/Cu/sub 1.7/O/sub x/ film and Tl-Ba-Ca-Cu-O bulk in Au foils, which are heated at 900 degrees C for 3 min in flowing oxygen followed by furnace cooling. The Tl-Ba-Ca-Cu-O films grown from the Tl-Ba-Ca-Cu-O bulks with Tl content of 3.5-6.5 mol.% consisted of the mixing phase of Tl/sub 2/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/, Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/, and Tl/sub 1/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/. These films have T/sub c/(R=0)=110 K.         Preparation and characterization of TI/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ Films on (100) LaAIO/sub 3/    W.L. Holstein, L.A. Parisi, D.J. Kountz, C. Wilker, A.L. Matthews, P.N. Arendt and R.C. Taber Summary: A two-step process for the fabrication of 0.12-1.20- mu m-thick TI/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films on (100) LaAlO/sub 3/ has been developed. The process involves the deposition of a BaCaCuO precursor film at low temperature by RF magnetron sputtering, followed by annealing in the presence of Tl/sub 2/O vapor to convert the precursor film into Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/. Over a distance of 4 cm, film composition was Tl:Ba:Ca:Cu=2.05+or-0.09:2.05+or-0.06:1.01+or-0.03:1.94+or-0.06, and thickness was uniform to within 6%. The films contain only trace quantities of secondary phases and are epitaxially oriented, with the c-axis of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ perpendicular to the surface and the two a-axes aligned with the pseudocubic a-axes of the underlying LaAlO/sub 3/ substrate. Films had a T/sub c/ for zero DC resistivity of 106.5+or-0.5 K, a transport critical current density for continuous current of 2.9*10/sup 6/ A/cm/sup 2/ at 4.2 K and 2.7*10/sup 5/ A/cm/sup 2/ at 77 K, and a sharp (<0.3 degrees C) AC inductance transition with an onset temperature of 105+or-2 K. Surface resistance at 20 GHz of less than 2 m Omega , about 10* lower than Cu, was routinely achieved for temperatures below 90 K and, for the best films, at temperatures up to 100 K. Surface resistance at about 10 GHz on one film was 0.067 m Omega at 4.2 K, 0.36 m Omega at 77 K, and 0.74 m Omega at 90 K. Films have been reproducibly fabricated on substrates up to 2.54 cm/sup 2/.         Superconducting properties of Tl-Ba-Ca-Cu-O films on silver substrates    R.C. Dye, P.N. Arendt, J.A. Martin, K.M. Hubbard, N. Elliott and G. Reeves Summary: Films of Ba-Ca-Cu-O have been RF-magnetron-sputtered onto Consil 995 substrates. A postdeposition anneal in an overpressure of Tl produces the superconducting 1212 and 2212 phases. Varying the annealing procedures changes the electrical properties of the final films dramatically. Dynamic impedance, a novel approach to the electrical characterization of these films on a conductive substrate, is discussed and compared with SEM (scanning electron microscope), XRD (X-ray diffraction) and RBS (Rutherford backscattering) measurements as a function of differing annealing protocols. The improvement in the superconducting responses as a function of annealing procedures correlates well with the improved morphology observed in the SEM photographs. Also, the XRD data show increased c-axis material with the C annealing protocol.         Transition properties of 2D granular thin films of Bi-Sr-Ca-Cu-O    T. Akeyoshi, T. Akiyama, H. Yashiro and M. Sugahara Summary: The I-V relations of granular Bi-Sr-Ca-Cu-O thin films have been investigated. It is demonstrated that the electrical properties can be classified into two groups according to their sheet resistance. Films with lower sheet resistance show superconductive transition, where the Kosterlitz-Thouless (K-T) effect with respect to the flux soliton has been observed in the resistive transition. Films with higher sheet resistance show sharp resistivity increase at low temperature; their properties are explainable based on a new K-T effect with respect to the charge soliton.         Highly oriented Bi-based thin films with zero resistance at 106 K    W. Kula, R. Sobolewski, J. Gorecka and S.J. Lewandowski Summary: The authors report on the fabrication and characterization of nearly single-phase superconducting Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ thin films. The films are DC-magnetron-sputtered from heavily Pb-doped (Pb/Bi molar ratios up to 1.25), sintered targets on unheated MgO, SrTiO/sub 3/, CaNdAlO/sub 4/, and SrLaAlO/sub 4//sur single crystals. For the films grown on the (100)-oriented MgO substrate, less than 1 h of annealing in air at 870 degrees C was sufficient to obtain more than 90% of the 110-K-phase material, with highly c-axis-oriented crystalline structure and zero resistivity at 106 K. The films fabricated on the other substrates also exhibited a narrow superconducting transition and were fully superconducting above 100 K, but they consisted of a mixed-phase material with a large percentage of the 80 K phase.         Ion beam deposition of high T/sub c/ superconducting thin film in the bismuth system    H.S. Huang, W.Y. Pan, B.B. Tang, Y.C. Yang, M.L. Liu, Y.Z. Liu, S.N. Mao, S.Z. Cai and K.S. Zhang Summary: Processing for the preparation of superconducting thin films by ion-beam sputtering is discussed. The main factors affecting the composition of the as-deposited films are analyzed, and the effects of various heat treatments on the properties of annealed films are studied. Superconducting BiSrCaCuO films on SrTiO/sub 3/ substrates with an onset temperature of 115 K and a zero-resistance temperature of 78 K were successfully prepared. The films had apparent c-axis texture. By adopting a Pb layer diffusion method, Bi(Pb)SrCaCuO films with a high-T/sub c/ phase were obtained.         Epitaxial films of 'BSCCO' grown from liquid KCl solutions onto several substrates    G. Balestrino, V. Fogliette, M. Marinelli, E. Milani, A. Paolette and P. Paroli Summary: A liquid-phase epitaxy growth technique (LPE) was used to obtain truly epitaxial BSCCO films on SrTiO/sub 3/ and LaGaO/sub 3/ substrates. Single-phase samples of the 2201 and of the 2212 phase have been grown. The growth liquid is a saturated solution of the BSCCO constituent oxides in KCl, and a suitable thermal gradient allows chemical transport from the solute to the substrate. The films have a mirror-like surface, small mosaic spread, and thicknesses of up to a few microns. The as-grown samples are fully superconducting. The typical resistance-vs.-temperature curve shows a metallic behavior down to about 80 K, followed by a narrow superconducting transition, with zero resistance reached at about 75 K. The transport properties of the films have been investigated and found to be heavily dependent on the substrate chosen; in particular, films grown on LaGaO/sub 3/ have much higher resistivities and much lower critical currents than those grown on SrTiO/sub 3/ substrates. These differences are shown to be due to the presence of weak links occurring in correspondence with twinning domain boundaries of the LaGaO/sub 3/ substrates.         DC reactive magnetron sputtered NbN thin films prepared with and without hollow cathode enhancement    D.F. Dawson-Elli, C.A. Fung and J.E. Nordman Summary: A comparison was made between NbN thin films prepared with and without hollow cathode enhancement of DC reactive magnetron sputtering. The hollow cathode arc source is used in a triode configuration with the magnetron. This design allows sputtering to take place at pressures as low as 5*10/sup -4/ torr and has been shown to improve process control in the sputtering of oxides from metal targets. These films were investigated for application in NbN Josephson junctions. Film deposition parameters have been related to growth rate, stoichiometry as measured by Auger electron spectroscopy (AES), transition temperature, growth texture as measured by X-ray diffraction (XRD,), and ellipsometric parameters. The relationships were investigated using factorial experimental design. An important pressure-power interaction which leaves T/sub c/ nearly invariant was observed. This interaction is explained in terms of the counteracting effects of ion bombardment. The maximum T/sub c/'s achieved were 14.18 K and 14.75 K with and without the use of the hollow cathode, respectively. The data suggest that the effect of the hollow cathode is to increase ion bombardment of the substrate, at least when used with small magnetrons.         YBa/sub 2/Cu/sub 3/O/sub 7- delta //insulator multi-layers for crossover fabrication    J.A. Beall, M.W. Cromar, T.E. Harvey, M.E. Johansson, R.H. Ono, C.D. Reintsema, D.A. Rudman, S.E. Asher, A.J. Nelson and A.B. Swartzlander Summary: The development of thin-film dielectrics compatible with the epitaxial growth of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) is crucial to the fabrication of multilayer device and circuit structures. The authors investigated the YBCO/SrTiO/sub 3/ (STO) system by fabricating YBCO/STO bilayers and simple YBCO/STO/YBCO crossover structures. The thin films were deposited in situ by pulsed-laser deposition and analyzed using X-ray diffraction and scanning electron microscopy. The film interfaces were characterized by secondary ion mass spectrometry (SIMS) depth profiling. The authors have developed photolithographic and wet-etching processes for patterning the crossovers which are compatible with these materials. The crossover structures were characterized by resistance and insulator pinhole density as well as by the superconducting properties of the patterned top and bottom YBCO electrodes (critical temperature, T/sub c/, and critical current density, J/sub c/). Using SrTiO/sub 3/ as the insulating layer, crossovers were made with good isolation between layers (>100 M Omega ) and high J/sub c/ even in the top electrode (J/sub c/(76 K)>10/sup 5/ A/cm/sup 2/).         PrBa/sub 2/Cu/sub 3-y/Nb/sub y/O/sub 7-z/ insulating films for YBa/sub 2/Cu/sub 3/O/sub 7-y/ based high T/sub c/ electronics    C.T. Rogers, A. Inam, R. Ramesh, J.-M. Tarascon, K. Remschnig, B.J. Wilkins and D.L. Hart Summary: The structural and transport properties of thin films of the insulating perovskite PrBa/sub 2/Cu/sub 3-y/Nb/sub y/O/sub 7-z/ (PrBCNO for y=1) were characterized. This material is a promising candidate for applications requiring high-quality epitaxial insulating layers in YBa/sub 2/Cu/sub 3/O/sub 7-y/ thin-film circuits: PrBCNO is nearly tetragonal with <2% lattice mismatch to YBCO, thus allowing the possibility of epitaxial multilayer growth. PrBCNO single films and PrBCNO-YBCO multilayers have been grown using pulsed-laser deposition: growth conditions typical for YBCO result in highly c-axis-oriented PrBCNO films and multilayers on a variety of (001) substrates. Preliminary measurements show a PrBCNO resistivity of >10/sup 5/ Omega -cm and an optical index of refraction of 2.25 at room temperature for y=1.         Properties of epitaxially grown A-axis oriented YBa/sub 2/Cu/sub 3/O/sub 7-x/-PrBa/sub 2/Cu/sub 3/O/sub 7-y/ heterostructures    A. Inam, R. Ramesh, C.T. Rogers, B. Wilkens, K. Remschnig, D. Hart and J. Barner Summary: Multilayer structures of YBa/sub 2/Cu/sub 3/O/sub 7-x/-PrBa/sub 2/Cu/sub 3/O/sub 7-y/ were prepared, using pulsed laser deposition, with the a-axis oriented normal to the surface of a variety of (001) substrates. Structural characterization of these films by X-ray diffraction, transmission electron microscopy, and helium ion beam channeling reveal a highly ordered microstructure similar, if not better, in quality to that obtained in the best c-axis-oriented films. Studies of the surface morphology by scanning electron microscopy show a very smooth surface with a total absence of the outgrowths commonly seen in c-axis-oriented films. It is observed that while the a-axis-oriented films grown on (001) substrates show no a-b axis twinning, the films are composed of 0.01-0.1- mu m-sized domains that have the Y(Pr)Ba/sub 2/Cu/sub 3/O/sub 7-x/ c-axis oriented along the substrate (100) or (010) in-plane direction. Superconducting transition temperatures, for current transport in the plane of the films, consistently exceed 80 K and are found to increase with the size of the domains.         Epitaxial growth of YBCO/MgO/YBCO structures    S. Tanaka, H. Nakanishi, T. Matsuura, K. Higaki, H. Itozaki and S. Yazu Summary: A Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-y/(YBCO)/MgO/Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-y/ structure on a MgO (100) substrate was prepared, and its crystallographic structure was investigated by cross-sectional transmission electron microscopy (TEM). A MgO ultrathin film with (100) orientation as an intermediate layer was obtained on each of the (001) and (100) YBCO thin films at a substrate temperature of about 400 degrees C. The crystallinity of the MgO layer was investigated as a function of the MgO thickness. The randomness of the crystallinity decreased with a decrease in the thickness. A (100) epitaxial MgO layer without other orientation was obtained at a thickness of 10 nm. From the results of cross-sectional TEM observation, it was found that the thickness of the MgO can be reduced to 5 nm at a minimum. In the sample with a MgO thickness of 5 nm, sharp interfaces were observed without any disrupted portion. When the thickness was reduced to 2 nm, the interface between the top layer and the base layer was crushed.         Magnetoconductance oscillations in high temperature superconducting networks    P. Fluckiger, V. Marsico, P.K. Srivastava, C. Leemann and P. Martinoli Summary: The complex AC impedance Z of superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ triangular networks exposed to a perpendicular magnetic field was measured with a two-coil mutual inductance technique. At temperatures close to the transition temperature, both the imaginary and the real parts of Z as a function of the magnetic field show oscillations resulting from flux quantization in the unit cell of the network. The limited number of oscillations observed is probably an indication of the reduction of the superconducting phase coherence by disorder and inhomogeneities in the network.         Morphology of silver on YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films    A. Roshko, R.H. Ono, J.A. Beall, J. Moreland, A.J. Nelson and S.E. Asher Summary: The morphology of silver layers deposited and annealed on laser-ablated YBa/sub 2/Cu/sub 3/O/sub 7- delta /, films was examined. Silver was found to dewet the YBa/sub 2/Cu/sub 3/O/sub 7- delta / (001) surface on annealing in oxygen and nitrogen. This dewetting behavior may be kinetically inhibited using either thick silver layers or short anneals and low temperatures. Silver layers 70-nm to 2.5- mu m thick were studied in films deposited on SrTiO/sub 3//sur, LaAlO/sub 3/, and MgO substrates. Anneal times were varied from 6.5 min to 15 hr at temperatures from 200 to 700/spl deg/C.         Development of superconducting electrode capacitor using a YBa/sub 2/Cu/sub 3/O/sub 7-x/ thick film and Y/sub 2/BaCuO/sub 5/ dielectric    W.K. Jones, R.A. Olmedo, Z.Q. Hu and G. Larkins Jr. Summary: Different phases in the YO/sub 1.5/-BaO-CuO phase diagram were evaluated for dielectric properties and compatibility with subsequent firing of a YBa/sub 2/Cu/sub 3/O/sub 7-x/ thick film. Y/sub 2/BaCuO/sub 5/ (211) was chosen for capacitor manufacture because it showed no reaction with the YBa/sub 2/Cu/sub 3/O/sub 7-x/ (123) thick film upon sintering. AC field exclusion confirmed the superconductivity of the 123 thick film on the 211 substrate with T/sub c/ at 93 K. Scanning electron microscopy of the interface between the 211 substrate and the 123 thick film showed neither a reaction nor the formation of a third phase. Capacitor samples were manufactured in various sizes. All sizes were found to have the following characteristics. For a range from 0.1-110 MHz, at 77K, the phase angle of the impedance remains constant at -90 degrees . The same is true at 298 K. This would be an improvement over a commercial chip capacitor for which the curve is constant only for a small range. The dielectric constant remains at 24 over the 0.1-110-MHz frequency range at 77 and 298 K. The capacitance of the sample was found to be constant over frequency. It is concluded that 211 substrates are suitable for the formation of a low-loss capacitor with superconducting electrodes.         Micropatterning of high-T/sub c/ superconducting film by nitrogen ion beam and Ta/resist multilayer mask    Y. Nagai, K. Tsuru, A. Terada and K. Yanagisawa Summary: Micropatterning of BiSrCaCuO/ss superconducting film is investigated for electronic devices. A combination of nitrogen ion beam and Ta/resist multilayer mask is found to be suitable for achieving micropatterns with sharp edges because of its high selectivity of more than 20. The resist layer enables high-resolution masks to be formed on relatively rough surfaces. Also, an Au protective layer successfully avoids the critical temperature degradation due to oxygen plasma. As a result, BiSrCaCuO microbridges, 1.5- mu m wide and 1- mu m thick, can be patterned without degradation of the critical temperature and critical current density. Accordingly, these patterning techniques are thought to be useful for fabricating SQUIDs (superconducting quantum interference devices) and microwave components.         Electrical properties of SN contracts with cleaved oxide superconductor films    I. Takeuchi, J.S. Tsai, H. Tsuge, N. Matsukura, S. Miura, T. Yoshitake, Y. Kojima and S. Matsui Summary: The authors have studied the feasibility of making sharp and clean electrical contacts with high-temperature superconductors by cleaving single-crystal Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films in a stream of evaporated noble metals forming SN (superconductor/normal metal) contacts at the revealed cross-sectional edge surfaces of the films. With this technique, contact resistances on the order of 10/sup -9/ to 10/sup -8/ Omega cm/sup 2/ have been consistently obtained. For a structure with an oxide/Au/oxide configuration, the interface resistance was found to show a flat temperature dependence below T/sub c/. Material dependence and anisotropy were observed in the contact resistance. When (110)-oriented films were cleaved in two perpendicular directions, surfaces normal to the c-axis gave interfaces with resistance more than one order of magnitude larger than the other direction. Bi-Sr-Ca-Cu-O/Au interfaces showed a tendency of giving slightly lower resistance than Y-Ba-Cu-O/Au interfaces.         YBa/sub 2/Cu/sub 3/O/sub x/-microstructures on semiconductor substrates    M. Schilling and U. Merkt Summary: Thin films of YBa/sub 2/Cu/sub 3/O/sub x/ were prepared by laser ablation with a KrF excimer laser on Si and GaAs. These films show degraded superconducting properties compared to films on SrTiO/sub 3/, which exhibit critical temperatures T/sub cO/=89 K and critical current densities J/sub c/(77 K) in the 10/sup 6/-A/cm/sub 2/ range. Critical temperatures of 57 K and 30 K for films on Si and GaAs, respectively, could be achieved. YBa/sub 2/Cu/sub 3/O/sub x/ microbridges on SrTiO/sub 3/ were prepared with widths down to 10 mu m by wet chemical etching or by laser ablation through metal masks. Patterning of films on bare Si, however, is complicated by microcracks in the film due to different lattice constants and thermal expansion coefficients of Si and YBa/sub 2/Cu/sub 3/O/sub x/. These problems may be overcome by the use of buffer layers, whose influence on the film quality is also discussed.         Growth of an Au layer with a thickness in the order of 10 nm on a Yb-Ba-Cu-O substrate    K. Takahashi, K. Shimaoka, M. Kamino, Y. Yoshisato and S. Nakano Summary: A Yb-Ba-Cu-O/Au structure for an S/N/S (superconductor/normal metal/superconductor) Josephson junction has been successfully fabricated using the bulk Yb-Ba-Cu-O substrate processed by the recently developed PMQ (plasma-arc melting and rapid quenching) method. The coverage of Au layers with a thickness of 30 nm at a substrate temperature of 600 degrees C was confirmed to be almost 100% without any pinholes, which is thin enough to make use of the proximity effect. Similar experiments using Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ single crystals indicated the possibility of high coverage at even lower substrate temperatures.         Preparation and properties of in-situ YBaCuO films on Si substrates with buffer layers    X.F. Meng, F.S. Pierce, K.M. Wong, R.S. Amos, C.H. Xu, B.S. Deaver Jr. and S.J. Poon Summary: High-T/sub c/ YBaCuO superconducting films have been prepared in-situ on Si substrates with buffer layers using off-axis single-target RF magnetron sputtering. A special cylinder heater with a reflecting cone was used to grow in-situ YBaCuO films on different buffer layers, such as Y-stabilized ZrO/sub 2/ (YSZ), LaAlO/sub 3/, LaGaO/sub 3/, NdAlO/sub 3/, NdGaO/sub 3/, SrTiO/sub 3/, and MgO. The YBaCuO films on YSZ and LaAlO/sub 3/ buffer layers have T/sub c/(zero) of 84 K and 83 K, respectively. Films deposited at substrate temperatures above 650 degrees C have preferential orientation with c-axis perpendicular to the film surface. The films also show excellent surface smoothness up to atomic scale with a roughness of 5 AA. The qualities of the films as well as the dielectric properties of the substrate and buffer layers are favorable for microelectronic applications, especially for high-frequency applications. High-T/sub c/ microbridges have been fabricated using the films.         As-deposited high T/sub c/ superconducting thin films on ITO-coated glass    K. Fujino Summary: High-T/sub c/ superconducting (HTSC) thin films deposited on a glass substrate coated with an oxide buffer layer have been studied without subsequent postanneal. The structure (HTSC/ITO/glass) came to be composed entirely of oxide materials. The deposition of the superconducting films was carried out by either excimer laser ablation or sputtering below the substrate temperature of 750 degrees C. The ITO buffer layer inhibits interdiffusion between YBaCuO and SiO2 and does not cause any cracks. The YBaCuO thin films were grown on ITO-coated glass oriented with the c-axis. The zero-resistivity transition temperature (T/sub c/) reached 80 K. ITO is considered a unique candidate for the stabilizer because of its transparence and electrically conductive properties. The structure of the superconducting film on ITO should be useful in industrial fabrication of superconducting plates, coils, and optoelectronic devices.         High T/sub c/ S-I-S and S-N-S structures using RF sputtered films    A.J. Drehman, B.L. MacDonald, R.J. Andrews and P.M. Tedrow Summary: Crosses consisting of 150- mu m-wide lines of Y-Ba-Cu-O separated by layers of yttrium-stabilized zirconia about 30-nm thick have been formed using RF diode sputtering and wet chemical patterning. The resistivity of the insulator has been measured as a function of temperature and was found to increase exponentially as the temperature was lowered, reaching values of 10/sup 9/ Omega -cm at 225 K. S-N-S (superconductor/normal metal/superconductor) structures have been fabricated from these crosses by ion-milling a 100- mu m-diameter hole through the junction region and depositing Au in the resulting via. After annealing in O/sub 2/ at 450 degrees C, the gold supports a supercurrent of up to 1.5 mA at 4.2 K, corresponding to a current density of about 3*10/sup 3/ A/cm/sup 3/.         Superconducting tapes with critical current density of 10/sup 4/ A/cm/sup 2/ at 77 K and zero magnetic field    E. Narumi, L.W. Song, S. Hwa, J. Ye, F. Yang, Y.H. Kao, S. Patel, D.T. Shaw and J.E. Rkaczyk Summary: A critical current density above 10/sup 4/ A/cm/sup 2/ at 77 K and zero magnetic field has been achieved for both YBa/sub 2/Cu/sub 3/O/sub 6.8/ (YBCO) thin films on metallic substrates and Bi-based superconducting films on silver tapes. A transition buffer, consisting of subbuffers deposited at different temperatures, was used to enhance the crystallinity and the transport properties of YBCO films on metallic substrates. YBCO films were fabricated using in-situ laser deposition, and they were strongly c-axis oriented. A critical temperature of 87 K and a critical current density of 3*10/sup 4/ A/cm/sup 2/ at 77 K were obtained for a 0.5- mu m-thick YBCO film. The magnetic field dependence of J/sub c/ could be increased by using Pt-coated metallic substrates. For 10-20- mu m-thick Bi-based superconducting tape, by using a brush-on technique and heat treatment, a critical current of 10/sup 4/ A/cm/sup 2/ at 77 K was obtained. This tape showed strong magnetic flux pinning at low temperature.         Oxygenation of silver clad YBa/sub 2/Cu/sub 3/O/sub 7- delta /    M.J. Neal and V.M. Pathare Summary: The effects of time, temperature, and coating thickness on the oxygenation of silver-coated YBa/sub 2/Cu/sub 3/O/sub 7- delta / wire during a postprocessing anneal were examined. Two different grades of silver-coated wire as well as bare ceramic fiber were subjected to a variety of isothermal and continuous-cooling oxygen anneals. DC transport J/sub c/, AC magnetic susceptibility, optical microscopy, and scanning electron microscopy were used to characterize the samples. It is expected that a continuous-cooling anneal will be more efficient than an isothermal anneal for oxygenating YBa/sub 2/Cu/sub 3/O/sub 7- delta /. Reasons for this assumption are examined, and results of both types of anneals are presented. The superconducting behavior of sintered YBa/sub 2/Cu/sub 3/O/sub 7- delta / is limited by weak links. Both the J/sub c/ and AC susceptibility data measure flux motion in the weak links and therefore both of these measurements are appropriate means of assessing the efficiency of oxygenation. The rate of oxygenation at high temperatures is an important factor in determining optimal continuous-cooling anneals. Susceptibility measurements were used to characterize this oxygenation. The presence of a porous silver cladding slows the rate of oxygenation of YBa/sub 2/Cu/sub 3/O/sub 7- delta / but does not change its basic character.         The magnetic stability of face-cooled composite tape superconductors    M. Chiba, T. Ogasawara, N. Miyazawa, S. Ban, Y. Kubota and K. Yasohama Summary: The concept of face-cooled composite tape is proposed to stabilize high critical current densities in Nb/sub 3/Sn, V/sub 3/Ga, and oxides. The stability is promoted by the combined action of the dynamic stability and the transient cryogenic stability. The expression of the limiting current density of stability is derived as a function of pertinent parameters of the superconductor, stabilizing normal metal, and coolant. An experimental proof of the analysis is given for an Nb/sub 3/Sn-Cu system. The specimens are made by alternately stacking strips of Nb/sub 3/Sn and copper. Stability is estimated by observing flux jumps for specimens of different thicknesses of copper. The experimental results agree well with the analysis. and an overall current density of about 500 A/mm/sup 2/ is stabilized. The concept of face-cooled composite tape will offer a useful basic criterion in designing conductors of high-T/sub c/ oxides.         Critical currents and the effects of pinning    A.M. Campbell Summary: The bulk magnetic properties of sintered materials are treated as those of a standard magnetic material with a permeability dependent on the porosity. If J/sub c/ is expressed as a function of the internal H instead of the applied field, it is much more constant. The flux profile technique can then be used to extract J/sub c/(B) at much lower fields than in bulk samples. A zero temperature flux creep mechanism is proposed but appears to be too small for the present computer simulation to detect. The effects of cobalt doping show that J/sub c/ is related to the depairing current. Increasing the coherence length decreases both inter- and intragrain critical currents, which are found to be affected in the same proportion. The causes of granularity and rapid flux creep are discussed, and it is concluded that there is no consistent explanation.         Author Index (1990 - Part 1)    No author information available Summary: Not available

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