A synchrotron x-ray powder-diffraction study has been carried out on two samples with well-defined excess oxygen concentrations, δ = 0.045 and 0.055. Evidence for one-dimensional interstitial oxygen ordering along the c -axis was observed from the appearance of a pair of superlattice satellite peaks at (0, 1,2 ± Δ) in both samples. In La2CuO4.045, a ∼5% oxygen-poor Bmab phase coexists with a stage-6 phase and with a small amount of the high-temperature-tetragonal (HTT) phase below the phase separation temperature (∼280 K). La2CuO4.055 shows a single stage-5 phase below 170 K, but with two unindexed peaks between (0, 1, 2 ± 0.2) satellites which may well result from a further domain modulation. The critical temperature Tc is increased by 1.5 K by reducing the stage number from 6 to 5.

Bisethylacetoacetato Cu(II), referred to as Cu(etac)2, was synthesized and used as a novel metal-organic precursor to produce Cu films by PECVD processing. Cu(etac)2 is a nonfluoride compound that is solid at room temperature with reasonable volatility at 120–150 °C of 0.8 Torr. Effects of selected process variables on the characteristics of Cu film deposition were studied. Considered variables were plasma power, hydrogen flow rate, deposition time, substrate temperature, and precursor temperature. The process conditions to give Cu films of a high quality were determined. The electrical resistivity approached 2 μΩ · cm as the Cu film thickness became greater than 2500 Å. The conformality of the Cu film deposition by PECVD was sufficient to result in complete via-hole fillings of wafers patterned for 256 Mb DRAM.

The superconducting filaments in (Bi, Pb)2Sr2Ca2Cu3Ox/Ag composite tapes have been imaged directly through the outer silver sheath of an unpolished tape by means of a magneto-optical imaging technique. The images reveal the morphology and alignment of the uppermost layer of filaments located as much as 112 μm below the unpolished tape surface, the depths of these filaments, and the homogeneity of the magnetic flux distribution within these filaments. These results demonstrate that the magneto-optical technique is a valuable nondestructive tool for analyzing (Bi, Pb)2Sr2Ca2Cu3Ox composite tapes.

A novel technique has been developed for simultaneous combustion synthesis and consolidation of intermetallics in a single step from elemental powders. The method has been applied for the synthesis and consolidation of MoSi2. A temperature profile of the combusted compact provides the temperature-time regime for consolidation. The products were characterized for density, phase formation, and microstructure.

Thermal conversion of acetate-derived gels to YBa2Cu3Ox (Y–123), Bi2Sr2CaCu2Ox (Bi–2212), and (Bi, Pb)2Sr2Ca2Cu3Ox (Bi-2223) has been studied by thermal analysis, x-ray diffraction, and infrared spectroscopy. Carbonates formed above 200 °C during thermal treatment of all gels. Decomposition of the carbonates proved to be more difficult for Y-123 than for Bi-2212 or Bi-2223. However, all of the gels that were heated contained significant amounts of carbon after calcination. Complete decarbonization of materials was attained by treating the intermediate phases (e.g., those formed after calcination at 600 °C) with nitric acid and then subjecting them to a final thermal treatment. Removal of carbonates from the intermediate phases strongly accelerated formation of the superconducting compounds.

We report here on the appearance of a hysteresis in the current-voltage characteristic, when a voltage is applied to a GdBa2Cu3O7−δ rod at room temperature. This hysteresis was caused by the appearance and disappearance of a hot spot. When a gradually increasing dc voltage (0–8 V) was applied to a GdBa2Cu3O7−δ rod, a hot spot appeared at a given voltage, Va. Further increasing of the voltage increased the spot size, while the current stayed constant. When a voltage of 8 V was reached, the voltage was gradually decreased. The spot did not disappear at Va, but at a voltage 0.2 to 1.3 V lower than Va. The current remained constant until the spot disappeared. By the authors' best knowledge, this is the first report of a hysteresis in the current-voltage characteristic at room temperature for a high Tc superconductor.

A novel thermomechanical processing technique for the synthesis of bulk submicron grain (grain size ≈200 nm) 304 stainless steel is reported. This ingot-metallurgical technique requires a total deformation of only 95%, and the key steps to this processing technique involve (i) formation of ultrafine dislocation cell structure, and (ii) the conversion of dislocation cells into grains with medium to high misorientation by grain boundary sliding.

The ability to process large grain, uniform high temperature superconducting ceramics that exhibit high critical current densities at 77 K is essential if the enormous potential of these materials for a range of permanent magnet-type applications is to be realized. We report a study of the fabrication of large grain YBa2Cu3O7−δ by seeded peritectic solidification in which key processing parameters such as the peritectic melting process, the seed-YBCO reaction, and the YBCO solidification kinetics are investigated in detail. Evolution of the sample microstructure during various stages of the growth process, in particular, has been studied extensively. The superconducting properties of specimens cut from different regions of large grain samples have been measured using vibrating sample magnetometry, and the results correlated with the microstructure of the materials.

Highly in-plane aligned α-axis YBa2Cu3O7−x thin films deposited on (100) LaSrGaO4 substrates by a self-template method were studied by high-resolution electron microscopy along three orthogonal 〈100〉 axes of the substrate. Plan-view images confirm that the majority of the film preferentially aligns across the entire substrate except for very few misaligned domains with average size 10 nm2. Cross-sectional images along the [100] orientation of YBa2Cu3O7−x reveal that in-plane aligned α-axis YBa2Cu3O7−x is grown on a template layer dominated by c-axis oriented film. This strongly suggests that the in-plane alignment of α-axis YBa2Cu3O7−x thin films on (100) LaSrGaO4 substrates is governed by the different stresses along the b and c axes of the substrate. Cross-sectional images along [001] of the YBa2Cu3O7—x thin film reveal that the 90° domains easily nucleate in the region between α-axis YBa2Cu3O7—x and the YBa4Cu3Ox phase. Cracks along the (001) plane of YBa2Cu3O7−x are found to be due to the large mismatch between the c parameters of the thin film and substrate.

In this study, we described the first results from an x-ray reflectometer which has been modified from an existing Kratky small angle x-ray scattering (SAXS) camera at the UNM/Sandia scattering center. Typically, seven orders of magnitude of reflectivity can be obtained over a range of 0.02 to 0.5 Å−1 in q. This allows the resolution of surface features of 10 to 1000 Å. The conversion to reflectometer is reversible and can be achieved in a short time, allowing for dual use of an existing Kratky camera.

A peritectic solidification growth model considering both solute diffusion in the liquid and interface kinetics is developed for the growth of YBa2Cu3O61x (123) superconductive oxide. The effect of interface kinetics on the growth rate and the rate control process is discussed using this model. The growth rate of the 123 crystal is evaluated as a function of the undercooling using the proper kinetic equation. The evaluated results by this model show good agreement with the experimental results. As a result of this evaluation, the growth of the 123 crystal is predicted to be limited by a mixed control process in general.

Formation of mullite on ceramic substrates via chemical vapor deposition was investigated. Mullite is a solid solution of Al2O3 and SiO2 with a composition of 3Al2O3 · 2SiO2. Thermodynamic calculations performed on the AlCl3–SiCl4–CO2–H2 system were used to construct equilibrium chemical vapor deposition (CVD) phase diagrams. With the aid of these diagrams and consideration of kinetic rate limiting factors, initial process parameters were determined. Through process optimization, crystalline CVD mullite coatings have been successfully grown on SiC and Si3N4 substrates. Results from the thermodynamic analysis, process optimization, and effect of various process parameters on deposition rate and coating morphology are discussed.

The enthalpies of formation and the partial molar enthalpies of oxidation of polycrystalline LnBa2Cu3Oy (Ln = Pr, Nd, Eu, Gd, Dy, Ho, Tm) and Y1−xPrxBa2Cu3Oy (x = 0.0, 0.1, 0.2, 0.5, 0.8, 0.9, 1.0) have been determined at 298 K by drop-solution calorimetry. The thermodynamic characteristics of Pr123 follow the trends of the trivalent-ion-based Ln123 compounds. The thermodynamic data for the (Y,Pr)123 solid solutions show nonideal solution behavior, but no x-dependent valence instability. The superconducting critical temperatures and the enthalpies of oxidation of the (Y,Pr)123 solid solutions are linearly related.

A highly (111)-oriented, highly coalesced diamond film was grown on platinum (111) surface by microwave plasma chemical vapor deposition (MPCVD). Scanning electron microscopy and x-ray diffraction analyses revealed that the (111) diamond facets were azimuthally oriented epitaxially with respect to the orientation of the Pt(111) domain underneath, with the neighboring facets of diamond being coalesced with each other. The film was confirmed as diamond using Raman spectroscopy.

Crack path stability is discussed, and it is shown that the standard continuum mechanics -force on a crack is the correct driving force for a crack. In a glass, where all cleavage planes are possible, this criterion also implies a path where the local Mode II on the crack is nullified.

Time-resolved in situ neutron powder diffraction and Rietveld refinement have been used to study the synthesis of Bi-2212 from hydroxide precursors in a 2% O2 atmosphere. Bi-2212 was found to form within the temperature range 770–800 °C. Studies at 800 °C show that Bi-2212 grows rapidly at the expense of Bi-2201. Upon lowering the temperature to 500 °C and changing the atmosphere to Ar, a rapid increase in the lattice parameters was observed. We attribute this change to the loss of oxygen from the Bi-2212 lattice. The final material exhibited a Tc of 94 K.

The electrical resistivity property of RuO2 thin films grown on the SiO2/Si substrate by reactive dc sputtering was examined in terms of microstructure using x-ray diffraction and cross-sectional transmission electron microscopy. As the samples were annealed in the oxygen ambient over the temperature range 300–700 °C, the resistivity decreased from 270 to 90 μΩcm with increasing annealing temperature. When heat treatment was performed below 500 °C, the strain which accumulated in the RuO2 layer during deposition was released without significant increase in grain size. It is thought that below 500 °C improvement in the crystallinity plays an important role in the variation of the resistivity. Although a considerable amount of growth of RuO2 grains was achieved, the columnar structure of the RuO2 layer in the as-deposited sample remained unchanged even after annealing at 700 °C. The resistivity improvement above 500 °C was driven mainly by the grain boundary annihilation.

Ultrafine silicon carbide powder with an average particle size of 90 nm was densified by hot-processing with the addition of Al2O3, Y2O3, and CaO at 1750 °C. Silicon carbide nanoceramics with an average grain size of 110 nm were prepared by liquid phase sintering at low temperature. The materials showed superplastic deformation at a strain rate of 5.0 × 10-4/s at 1700 °C, which is the lowest temperature published. The microstructure and deformation behavior of materials from a submicrometer powder were also investigated as a reference.

The effect of thickness on methanol transport in fourteen-year-old crosslinked poly(methyl methacrylate) was investigated. The samples studied here are from the same primary source of those used by a study made fourteen years earlier. The sample was encapsulated by a plastic bag and maintained in a desiccator at room temperature. Four thicknesses, 0.6, 1.0, 1.5, and 1.9 mm, were examined. Methanol sorption data were fit to a model in which the mass sorption is a combination of case I, case II, and anomalous sorption. The diffusion coefficient for case I transport increases with increasing thickness, but the velocity for case II transport does the opposite. The diffusion coefficient for case I transport and the velocity for case II transport exhibit the Arrhenius behavior. The activation energies for case II transport are 18.9, 16.3, 14.6, and 13.4 kcal/mole, corresponding to the thicknesses 0.6, 1.0, 1.5, and 1.9 mm, respectively. The activation energies for case I transport are 24.7, 24.2, 21.7, and 21.9 kcal/mole, corresponding to the thicknesses 0.6, 1.0, 1.5, and 1.9 mm, respectively. For thickness 1.5 mm the activation energies for case I and case II transport are 21.7 and 14.6 kcal/mole for this study and 24.9 and 17.3 kcal/mole obtained fourteen years ago.

A cyclic heat-treatment process was used to prepare single grains of the quasicrystalline icosahedral phase, ψ–Al65Cu23Fe12. Alloys of appropriate composition are melted and chill cast into copper molds. Multiple cyclic heat treatments at successively higher temperatures below 860 °C, the peritectic decomposition temperature of the quasicrystal phase, are used to enhance the growth of the ψ phase. Single grains up to 10 mm × 5 mm × 5 mm have been prepared.