We studied the electrical current induced superconducting-resistive transitions in laser deposited c-axis oriented crystalline Y1Ba2Cu3O7−x superconducting thin films. Comparative studies of I-V characteristics of thin film bridges with different geometries at temperatures below Tc and SEM voltage imaging of current induced resistive regions in the same samples were performed. The I-V curves of these bridges had two nonlinear regimes, a gradual and an abrupt transition to the normal state. We concluded that the gradual nonlinear transition is caused by imperfections in the sample such as film and substrate defects, film thickness variation, etc., and by dissipative effects such as flux motion and superconductor/normal-metal/superconductor type behavior. The abrupt transition to the normal state in the I-V curve is ascribed to Joule heating. The SEM mapping provides a direct image of the above effects and is useful for material or device characterization and for studying the transport properties of high Tc films.

Regular networks of localized grain boundary dislocations (GBDs) have been imaged by means of transmission electron microscopy in three different types of high-angle grain boundaries in YBa2Cu3O7-δ, implying that these boundaries possess ordered structures upon which a significant periodic strain field is superimposed. The occurrence of these GBD networks is shown to be consistent with the GBD/Structural Unit and Coincidence Site Lattice (CSL)/Near CSL descriptions for grain boundary structure. Thus, these dislocations appear to be intrinsic features of the boundary structure. The spacing of the observed GBDs ranged from ∼10 nm to ∼100 nm. These GBDs make the grain boundaries heterogeneous on a scale that approaches the coherence length and may contribute to their weak-link character by producing the “superconducting micro-bridge” microstructure which has been suggested on the basis of detailed electromagnetic measurements on similar samples.

High resolution electron microscopy of the twin boundary layers in YBa2(Cu1−xMx)3O7+δ for x = 0 and 0.02 and M = Zn and Al showed that the boundary widths are ∼1 nm for the pure and the Zn substituted YBa2Cu3O7 and ∼3 nm for the Al substituted oxide. From two beam contract studies and the high resolution images, it was concluded that the respective lattice plane across the boundary is shifted by (⅓–½)·2d(110) along the boundary. The broadening of the layer by the Al substitution is also thought to be a cause for the reduction of the twin boundary energy, leading to an increased twin density.

We have prepared BiSrCaCuO superconducting thin films by the pulsed laser evaporation method, using a YAG or an ArF excimer laser. The as-deposited films, which were enriched in Cu with respect to the bulk target composition Bi2Sr2Ca1Cu2O8 (i.e., the “2212” phase), were converted into the superconducting phase by a subsequent high temperature annealing in oxygen. Resistivity measurements showed superconducting transitions near 90 K, and the highest zero resistivity temperature was 83 K. The influence of the deposition parameters (photon wavelength) and annealing conditions (temperature, duration, and atmosphere) have been studied. The composition and in-depth distribution of the various elements were determined by Rutherford backscattering spectrometry (RBS), and the surface morphology was studied by scanning electron microscopy (SEM).

A process has been developed for the synthesis of YBa2Cu3O7−x superconducting fibers from an organic acid precursor solution. Through rheology measurements on a series of precursor solutions, the molecular structure was determined and subsequently controlled to allow for fiber drawing. For solutions with a viscosity ⋛10 poise, fibers of 1 to 2 m length and 50 ∼ 100 μm diameter can be hand drawn at ≍80 °C. Processing methods were developed to circumvent deformation of the thermoplastic fibers during heating and to minimize BaCO3 formation during decomposition. Fibers sintered at 850 °C for 1 h in 10−2 atm O2, followed by annealing at 500 °C for 4 h in O2, were fully dense, consisted of submicron grains, and were superconducting.

The mechanisms of metallic glass formation and competing crystallization processes in mechanically-deformed Ni-Zr multilayered composites have been investigated by means of differential scanning calorimetry and x-ray diffraction. Our investigation of the heat of formation of amorphous NixZr1−x alloys shows a large negative heat of mixing (on the order of 30 kJ/mole) for compositions near Zr55Ni45 with a compositional dependence qualitatively similar to that predicted by mean field theory. We find that the products of solid state reactions in composites of Ni and Zr can be better understood in terms of the equilibrium phase diagram and the thermal stability of liquid quenched metallic glasses. We have determined the composition of the growing amorphous phase at the Zr interface in these Ni-Zr diffusion couples to be 55 ± 4% Zr. We investigated the kinetics of solid state reactions competing with the solid state amorphization reaction and found the value of the activation energy of the initial crystallization and growth of the growing amorphous phase to be 2.0 ± 0.1 eV, establishing an upper limit on the thermal stability of the growing amorphous phase.

The hydration of YBa2Cu3O7-y in water vapor was investigated at various values of y and at two different PH2O by measuring the weight of the specimen. The reaction was relatively insensitive to the values of y and was extensive in the water vapor pressure of 2.7 kPa at room temperature and 140 °C. This was due to the decomposition of YBa2Cu3O7-y by reacting with H2O. The weight gain was also detected in the water vapor pressure of 270 Pa. The weight gain under lower water vapor pressure was supposed to be controlled by diffusion of OH− in YBa2Cu3O7-y. The diffusion coefficient calculated from the measurement was compared favorably with the oxygen diffusion coefficient.

Superconducting YBaCuO thin films have been fabricated on single-crystal MgO by the spray-pyrolysis of nitrate precursors. The effects on the superconductive behavior of processing parameters such as time and temperature of heat treatment and film thickness were investigated. The superconductive behavior was found to be strongly dependent on film thickness. Films of thickness 1 μm were found to have a Tc of 67 K while thinner films showed appreciably degraded properties. Transmission electron microscopy studies have shown that the heat treatments necessary for the formation of the superconductive phase (for example, 950 °C for 30 min) also cause a substantial degree of film-substrate interdiffusion. Diffusion distances for Cu in the MgO substrate and Mg in the film were found to be sufficient to explain the degradation of the superconductive behavior in films of thickness 0.5 μm and 0.2 μm. From the concentration profiles obtained by EDS analysis diffusion coefficients at 950 °C for Mg into the YBaCuO thin film and for Cu into the MgO substrate were evaluated as 3 × 10−19 m2/s and 1 × 10−17 m2/s, respectively.

Flux trapping in the 9.3 GHz modulated microwave absorption spectra observed near 4 K from ceramic and powdered ceramic specimens of two separately prepared YBa2Cu3O7-δ samples has been used to separate the intergranular and intragranular contributions to the spectra. In the denser, glassy sample, a broad absorption with a peak near 400 Oe for forward sweeps was observed with appreciable intensity after the maximum flux was trapped. This spectrum is attributed to intergranular junctions, since its relative intensity was reduced on powdering and suspending in wax. In the less dense, more uniform sample, the latter spectrum was appreciably weaker in both ceramic and powder. Both types of junction appear to contribute to the narrow low-field absorption which was observed after zero field cooling in all the samples.

The effect of heat treatment on microstructure development in Ba2YCu3O7−x films prepared from metal trifluoroacetate precursors is investigated. The growth of textured Ba2YCu3O7−x on BaZrO3 substrates is shown to be strongly influenced by the furnace atmosphere used during calcination. Differential thermal analysis was used to show that conditions that promote c-axis texture are also those which cause partial melting of Ba–Y–Cu–O compositions that are depleted in barium relative to Ba2YCu3O7−x.

High quality diamond thin films were deposited on different substrates at temperatures from 300 to 1000 °C by the microwave plasma enhanced chemical vapor deposition (MPCVD) system. The quality of deposited diamond films was improved by adding oxygen in the gas mixtures. Different ratios of methane to oxygen concentration in hydrogen at different temperatures have been studied. At high temperatures (800–1000 °C), the addition of oxygen will not only enhance the growth rate of deposited films but also extend the region of diamond formation. At low temperatures (<500 °C), the oxygen plays an important role in diamond film growth by preferentially etching the non-diamond carbon. Without the addition of oxygen, the films deposited at high temperatures (>900 °C) were either graphitic or diamond containing a large amount of graphitic or amorphous carbon and at low temperatures (<500 °C) were white, soot-like coatings which were easily scraped off. The quality of the deposited films was characterized by Raman spectroscopy and scanning electron microscopy.

Synthesis of YBa2Cu3O6+x from formic acid solutions of stoichiometric amounts of the initial materials has been investigated in the temperature range 750–950°C. The reaction is strongly influenced by the concentration of formic acid. Dilute solutions favor synthesis of purer samples under moderate conditions of temperature and sintering time. At lower temperature the same effect can be achieved if sintering time is longer, while at higher temperature, multiple grinding and heating at very short intervals are necessary to avoid formation of Y2BaCuO5. The observed effect of HCOOH concentration is explained by the different mechanisms involved in the decomposition of the formates obtained.

In order to obtain essential information on the formation process of the high-Tc phase in the Bi, Pb-Sr-Ca-Cu-O system, phase equilibria in the system PbO-CaO-CuO have been studied, mainly by x-ray diffraction analysis and thermal analysis. Temperature versus composition diagrams were established for the systems PbO-CuO(Cu2O) and PbO(PbO2)–CaO in air. Three invariant points were detected in these systems: a eutectic reaction (PbO + Ca2PbO4 = L) at 847 ± 6°C, a peritectic reaction (Ca2PbO4 = L + CaO) at 980 ± 2°C, and a eutectic reaction (PbO + CuO = L) at 789 ± 3°C. For the system PbO(PbO2)-CaO-CuO, subsolidus phase equilibrium in air was established. The liquidus was also examined at 780, 800, and 820°C, and a ternary (PbO-Ca2PbO4-CuO) eutectic point was detected at 772 ± 6°C.

Magnetic susceptibility measurements are used to show that the superconducting transition temperature of yttrium barium cuprate is lowered by carbon trapped in the microstructure of dense polycrystalline materials during sintering. We show that carbon is retained in the material as a result of the porosity closing off during the sintering process. X-ray photoelectron spectroscopy and electron energy loss spectroscopy are used to show that the retained carbon forms a solid solution with YBa2Cu3O7–δ and resides in a barium carbonate-like configuration in the crystal structure. The origin of the lowering of the superconducting transition temperature and processing strategies for preventing carbon retention are discussed.

A nonaqueous plating bath for silver deposition on the Ba2YCu3O7 superconductor has been modified with thiourea to give enhanced coverage of the metal film at low thicknesses. For both porous and high density ceramic substrates, SEM and optical microscopy show nucleation of silver deposits is increased by the additive. The resulting silver-superconductor contact resistances are comparable to those achieved without additives. Adhesion of the deposits and ease of mechanical handling are improved with thiourea. The combination of highly reactive oxidized substrate, nonaqueous solvent, and strongly surface active agent forms a novel extension for electrodeposition science.

Structural defects in thin films of nominal composition YBa2Cu3O7 (123) grown on single crystal MgO have been characterized. The main types of stacking defects correspond to the cationic stoichiometries of “248”, “247”, and “224”. Several types of edge dislocations have been observed. Due to the frequent changes in the stacking sequence, antiphase boundaries are created to accommodate the misfit across regions in which the repeat sequence is not identical. The films exhibit a mosaic microstructure due to the formation of grain boundaries in the a-b plane.

The ordered fcc intermetallic compound Ni3Al was mechanically milled in a high energy ball mill. The severe plastic deformation produced by milling induced transformations with increasing milling time as follows: ordered fcc → 2; disordered fcc → 2; nanocrystalline fcc + amorphous. The milling time for complete disordering occurred at 5 h for stoichiometric Ni3Al milled at ambient temperature compared to 50 h for the first observation of an amorphous structure. The structural and microstructural evolution with milling time was followed by x-ray diffraction, TEM, hardness, and calorimetry. The major defect believed responsible for inducing the crystalline-to-amorphous transformation is the fine grain boundary structure with nanometer (∼2 nm diameter) dimensions. The calculated interfacial free energy of the grain boundaries is consistent with the estimated free energy difference between the fcc and amorphous phases in Ni3Al.

Acoustic emission from sintered ceramic YBa2Cu3O7−x (YBCO) superconductor pellets provides a direct measure of microcracking behavior during processing. By detection and statistical analysis of acoustic events, the effects of cooling rates, processing atmosphere, average grain size, additives, and grain alignment on microcracking in YBCO have been studied. The onset temperature and duration of acoustic emission during cooling correlate well with the oxygen partial pressure in the furnace. Rapid changes in oxygen partial pressure at constant temperature produce acoustic emission that is characteristic of microcracking. A reported critical grain size for microcracking in sintered polycrystalline YBCO of about 1 μm has been confirmed. Two superconducting compounds, YSrBaCu3O7−x and LaBaCaCu3O7−x with the 123 structure but with smaller crystallographic anisotropy were also examined. Recommendations are made for minimizing microcracking during processing of superconducting ceramics.

Energy Dispersive X-ray Spectroscopy (EDS) was used to show that the elemental homogeneity of YBa2Cu3O7 powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950°C), followed by annealing in oxygen at 950°C, and slow-cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO2-treated powder, as measured by both ac and dc techniques. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO3)2, which acts as a flux that dissolves the constituents and reprecipitates them as high purity YBa2Cu3O7.

Surface hardening of SUS304 resulting from the process of doping and deposition of Si by irradiation of a KrF excimer laser beam in a SiH4 gas ambient is investigated, and variations of the surface hardness are examined for different numbers of laser pulses and the laser fluences. The hardening is due to Si incorporation in high concentration. The continuous distribution of Si atoms across the surface layer suggests that a very high adhesion strength of the deposited Si films can be formed. The specific process for surface modification is referred to as laser implant-deposition (LID).