The vortex dissipation in an Nd-Ce-Cu-Ol epitaxial film is measured at microwave frequencies using the high-Q modes of a sapphire ring resonator, over a large range of temperatures and external DC magnetic fields. The results are qualitatively consistent with a generalized thermally-activated flux-flow (TAFF) model.

Ultra-thin SiO2 barriers have been developed for application to the integration of thin films of YBa2Cu3O7−x (YBCO) superconductors to silicon. The SiO2 barriers are formed by the selective oxidation of Si with 2–5 ML yttrium overlayers. The Y-promoted SiO2, barrier formed by this technique is highly stoichiometric and is an effective buffer which prevents YBCO/substrate interdiffusion. The technique has been applied to YBCO on Si and has resulted in a YBCO transition temperature of TC=78°K for a 70Å Y-promoted SiO2 barrier.

This technique has also been applied to the growth of multilayer YBCO films and fabrication of SIS junctions. For this purpose, a Y-promoted SiO2 barrier was prepared by the selective oxidation of a Y/Si/Y sandwich layer grown on thin fdm YBCO deposited on MgO by standard laser deposition. This resulted in a 20–40Å SiO2/Y2O3-, high quality barrier. Following barrier preparation, a second YBCO thin layer was deposited on the barrier yielding a YBa2Cu3O7−x-SiO2-YBa2Cu3O7−x (SIS) structure which was then patterned to yield 100μm diameter SIS junctions. Voltage-current measurements across the SIS junction have shown Joseph son junction behavior.

We report on high quality Ba1−xKxBiO3 (BKBO) thin films grown by pulsed laser deposition. The best films exhibit resistive and magnetic transition temperatures of 28 K, with a transition width of 0.4 K and critical current densities above 106 A/cm2 measured at 5 K. Surface impedance is measured to be 1 mΩ. Films are single phase and highly oriented in the (100) direction and electron diffraction shows no other phases. Analysis using Moire' fringes shows films to consist of 100 nm size dislocation-free regions which show a high degree of in-plane epitaxy.

TlBA2Cu3Ox and Tl2Ca2Cu3Ox powders were synthesized, loaded into Ag tubes, and worked into wires and tapes by drawing and rolling. All processing outside of furnaces was in a dry-N2 glovebox. All heat treatments were performed in O2. The Ag-clad wires fabricated from these powders exhibited onset of superconductivity at ≈118 K and critical current densities at 77 K of 2 × 103 to 4 ×103 A/cm2.

The finite temperature properties of a two-dimensional flux lattice are studied by Monte Carlo simulation, with particular attention to the effects of twin-boundaries. The parameters selected are appropriate for the YBa2Cu3O7 high-temperature superconducting system. The intrinsic properties of the vortex state are investigated by monitoring system evolution at fixed temperature and applied magnetic field. By varying the temperature, the loss of type-II superconductivity via fluxoid lattice melting is also examined. The introduction of model defects induces the creation of metastable and glassy states which reduce overall hexatic order but are found to enhance system resistance to flux-lattice melting.

A technique is presented where Ag is initially sputter deposited on a single crystal ceramic substrate followed by in situ deposition of YBa2Cu3O7δ The resulting microstructure shows Ag islands amidst a c-axis oriented YBCO film, apparently with intimate contact between the YBCO and substrate. This morphology appears ideal for electrical contact to the {hko} surfaces of the superconductor with current carrying CuO planes in maximum contact with the Ag.

NASA's requirements for space-based cryogenic detector systems include the long-term storage of the liquid helium cryogen necessary for the optimized performance of far-infrared (IR) detectors. Significant heat loads on the liquid helium dewars exist due to the numerous electrical connections to the detectors, accounting for approximately 20 percent of the total heat load for some systems. High temperature superconductor lead assemblies are under development to replace the existing manganin wires connecting instruments at 80 K to the detector array at 4.2 K. These superconductive elements provide adequate current transport properties, while decreasing the thermal load on the liquid helium dewar. As a result, mission lifetimes can be extended by 10 percent or more.

Thick films of the superconductive material on low thermal conductivity substrates (e.g. yttria stabilized zirconia and fused silica) have been proposed to replace the existing lead assemblies. This work describes some of the design constraints on such a device as well as preliminary analyses of the effects of vibration, gamma irradiation, and long term exposure to high vacuum and liquid nitrogen encountered in operating such a device in space.

Infrared absorption measurements have been made in three kinds of Bi compounds of a high-Tc family mainly by making use of powdered samples. Two of them are superconductors with Tc's of 108 K and 82 K, respectively, and the remaining one is a semiconductor. In each of the superconducting compounds, there appears Mid-Infrared absorption band: No such absorption band is found in the semiconducting compound. At Far-Infrared region, many absorption peaks due to phonons are clearly detected in all of these samples. Some of the phonon modes have been identified. At very low energy region, free carrier absorption appears in superconductors. Only this part of the absorption shows a temperature dependence. Absorption intensity decreases as the temperature decreases.

By using the solid, liquid and vapor processes, such as doctor blade, laser pedestal growth, FZ, plasma spraying, ICB, CVD and laser ablation, wires and tapes were successfully fabricated. These experiments yielded the following results : Bi-2212 seven stranded wire with multi-layer structure by doctor blade method was prepared, and Ic of 270A (77K, OT) was achieved. Bi-2212 wires were prepared by laser pedestal growth, and Ic of 500A (77K, OT) was obtained in the case of 3mm in diameter. The a-b plane aligned Y-123 films-was deposited on Hastelloy, tape by laser ablation, and high Jc of 2.5×10 A/cm2 (77K, OT) and 2.2×10 A/cm2 (77K, 8T) were measured.

We have investigated the effect of substrate temperatures ranging from 680 °C to 800 °C on the orientation of pulsed laser deposited YBa2Cu3O7−x.(YBCO) thin films on (100) LaAlO3 substrates. X-ray diffraction studies indicate that there is a progressive change in the dominant orientation of the films from c-axis oriented (c-axis perpendicular to the substrate surface) to a-axis oriented (a-axis perpendicular to the substrate surface) grown as the substrate temperature is lowered. Two YBCO bilayers, which are the a-axis oriented YBCO film on the top of c-axis oriented YBCO film (a/c) bilayer and c-axis oriented YBCO film on the top of a-axis oriented YBCO film (c/a) bilayer, have been grown by in situ two step pulsed laser deposition and were characterized by scanning electron microscopy (SEM), Rutherford backscattering (RBS) spectrum, x-ray diffraction (XRD), and Tc measurements. Through SEM and XRD studies, double layer structures of the a/c and c/a bilayers were confirmed indirectly.

All-oxide S-N-S (superconductor-normal layer-superconductor) junctions having a planar structure are fabricated and their electrical characteristics in the normal state are investigated. The superconducting electrodes are composed of HoBa2Cu3O7−x, and the normal layer is La1.5Ba1.5Cu3O7-y. Conductance characteristics are measured and their behaviors are explained by the geometrical resonance of quasiparticles. A pair potential distribution in the normal layer is estimated from the resonance structure.

Interaction between vortices and inhomogeneity in superconductors is studied. As a typical example, we investigated the case of a single vortex and some vortices near an inclusion of the cylindrical shape and derived the interaction potential for the vortices as a function of the distance by use of the solution of London equation.

The time-dependent magnetic relaxation was measured in a full field penetrated YBa2Cu3O7-δ detwinned crystal for long times up to 5×105 sec. The relaxation data exhibit a power-law time dependence over a wide range of temperatures and magnetic fields indicative of flux creep with logarithmic dependence of the effective creep activation barrier U(J). A theoretical model is employed to analyze the data and to determine the activation energy.

The characteristics of YBa2Cu3O7−x (YBCO) thin films by laser ablation on MgO bicrystals have been investigated. The bicrystals were fabricated by hot pressing two single crystals with the configuration of [001] tilt boundaries. The YBCO films were epitaxial grown with C-axis normal to the both adjacent grains of bicrystals. The FWHM about (005) reflection was 0.4–0.5 degree, indicating the high degree of the oriention for the film with small mosaic spread. Our preliminary study showed that the typical value of Jc on either side of the bicrystal boundary was 0.4–10×106 A/cm2 at 15K, while that across the 10° tilt boundaries was 0.3–9×105 A/cm2 at 15K. These results implied that the artificial grain boundaries effectively weakened the supercurrent, and therefore, the weak-link properties of artificial boundaries were more easily controllable than those of naturally occuring grain boundaries.

Evidence of weak link effects in epitaxial thin films of YBa2Cu3O7-yon LaAlO3 is obtained from magnetically modulated resistance (MMR) measurements. This result suggests that weak links could provide a mechanism for the residual microwave loss in high quality superconducting thin films which contain predominantly low angle grain boundaries.

The microstructure of Y1Ba2Cu3Oy films and Y1Ba2Cu3Oy / Pr1Ba2Cu3Oy multilayers prepared by a pulsed organometallic beam epitaxy (POMBE) technique have been characterized by transmission electron microscopy (TEM). The microstructure of the films is observed to vary as a function of substrate temperature. At low temperatures, films are polycrystalline and exhibit some impurity phases. At higher substrate temperatures, films grow epitaxially with smooth surfaces and few impurities. Controlled growth at sufficiently high substrate temperatures allows uniform growth of alternating Y1Ba2Cu3Oy and Pr1Ba2Cu3Oy layers.

Crystalline bismuthates Ba1−xKxBiO3 with x greater than 0.5 are obtained by a low temperature anodic electrocrystallization method in a potassium hydroxide molten flux. The x = 0.56 bismuthate crystal shows 8K superconductivity determined by AC magnetic susceptibility.

Dc magnetic field, temperature, and magnetic history dependencies of the millimeter-wave surface resistance have been measured in high quality grain-aligned and in polycrystalline YBa2Cu3Ox bulk material. The measurements were carried at 75 GHz using the endplate of the cavity replacement method. The data is interpreted in terms of the presence of intra- and inter-grain types of weak links. The values of characteristic critical fields of the bulk and the weak link junctions are determined and discussed.

Crystalline quality of Bi-based oxide films has been evaluated by means of X-ray diffraction (XRD) and ion-channeling on the Rutherford backscattering (RBS). The films were sputter deposited 2201-phase Bi2Sr2Cu1O8-δ (BSCO) and 2212-phase Bi2Sr2Ca1Cu2O8-δ (BSCCO). They were prepared on MgO(100) and SrTiO3(100) substrates at the low temperature of 650°C during the deposition. The best quality, however thin films had poor crystallinity compared to single crystals, was obtained with the 2201-phase BSCO film that was deposited on a SrTiO3(100) substrate. The full width at half maximum (FWHM) value of the rocking curve on XRD for the film was estimated as 1560 (arc sec).

The deposition of large area multilayers with smooth surfaces is an important topic for the realisation of high quality multiturn coils for flux transformers. We have developed a co-sputtering process from two metallic targets for the deposition of large areas of extremely smooth YBaCuO thin films. Conditions for epitaxial growth of MgO layers on YBaCuO have been investigated. Epitaxial multilayers with good electrical properties (Tc,o > 82 K) have been fabricated.