A study of the prepolished surface of γ-TiAl specimens superplastically deformed in tension showed evidence of macroscopic surfaces at which grain boundary sliding occurs. In a scanning electron microscope these surfaces are observed as black bands on the deformed surface because of the difference in the appearance of these bands and grain regions situated in between these bands. It has been suggested that cooperative grain boundary sliding, i.e., sliding of grain groups, occurs during superplastic deformation, giving rise to these bands.

Stable conditions have been identified for two-zone processing of the superconducting thallium cuprate Tl0.5Pb0.5(Sr0.8Ba0.2)2Ca2Cu3Oy. With P(O2) of 0.8 atm, P(Tl2O) of 4.4 × 10−3 atm, and a sample temperature of 920 °C, single-phase Tl0.5Pb0.5(Sr0.8Ba0.2)2Ca2Cu3Oy, is produced with a Tc of 115 K, complete diamagnetic shielding, and Meissner fraction greater than 70%. Although a small amount of melting occurs under these conditions, a comparison of the low-field diamagnetic shielding for these samples with samples of Pb- and Sr-free TlBa2Ca2Cu3Oy and Tl2Ba2Ca2Cu3Oy, suggests that such melting is not necessary to produce the triple-CuO2-layer superconductors.

The mullite phase has been synthesized by subjecting a suitably chosen precursor gel to different pressure and temperature conditions. At ambient pressure mullite phase grows at a temperature of 1400 °C when the gel is heated for 2 h. At a pressure of 24 bar, on the other hand, similar growth occurs at a temperature of 750 °C for 5 min.

SiC whisker/calcium phosphate and C fiber/calcium phosphate composites were fabricated by hot-pressing at 1185 °C and 7.6 MPa in vacuum. The microstructural characteristics, especially interfaces, of these composites were studied using transmission electron microscopy. The mechanical properties of these composites were measured by four-point bending tests. It was found that the mechanical properties of these calcium phosphate-based composites were strongly dependent on their microstructural characteristics.

Nanometer-sized silver particles with diameters in the range 4.3 to 11.5 nm have been grown within a glass-ceramic containing BaTiO3 by just subjecting the former to an alkali/silver ion exchange reaction. A reduction treatment in hydrogen is, however, shown to be necessary for such growth in glass-ceramics having crystalline phases such as BaTiSiO5, Zn2SiO4, and Li4P2O7, respectively. The possible presence of Ti3+ ions in the BaTiO3 phase is believed to cause such a difference in the reduction behavior of these composites.

It was shown through two experiments that submicron-size pits formed on the surfaces of a dense fused quartz substrate and a Y2O3-ZrO2 ceramic thin film that were coated with gold and then heat-treated in air at 1200 °C. The formation of the pits is believed to be caused by the positive capillary pressure (approximately 22 MPa) generated in the molten gold droplets (<1 μm in diameter) that were formed as the gold coating melted.

Highly oriented diamond thin films grown on silicon via microwave plasma chemical vapor deposition were examined by transmission electron microscopy. In the plan view, defects appearing at the grain boundary were easily observed. (100) faceted grains that appeared to have coalesced were connected at their interfaces by dislocations characteristic of a low angle grain boundary. From Burgers vector calculations and electron diffraction patterns, the azimuthal rotation between grains was measured to be between 0 and 6°. The defect densities of these films are compared to reports from (100) textured randomly oriented films, and the relative improvement due to the reduction of misorientation and grain boundary angles is discussed.

Acetate, nitrate, and oxalate precursors for YBCO have been spray pyrolyzed under different conditions. Shelled and nonhollow microparticles were obtained from acetate and nitrate precursors, while nonhollow agglomerates were obtained from the oxalate suspension. At low furnace temperatures, the temperature and residence time of the particles were insufficient for complete decomposition of the precursors leading to Cu2O and Cu metal in the product. At 900 °C and above, reduced forms of CuO were not detected by x-ray measurements, and up to ∼60 wt.% YBCO was obtained. An approximate model predicting the particle and gas temperatures along the reactor under different operating conditions was developed. The model demonstrates that under the experimental conditions used here, the absorbed radiation heat by the particles from the furnace walls is significant in heating the gas. The gas and the particle temperatures are fairly close due to the effective heat transfer to the particles. At furnace temperatures of 700 °C, the maximum predicted particle temperature is about 500 °C (for ∼1 s). This explains the incomplete reactions obtained under these conditions. Above 900 °C the reactions are predicted to be complete within the first half of the furnace, leaving sufficient residence time for partial conversion into YBCO. Finally, an approximate expression predicting the relative contribution to the gas heating by the walls and the aerosol has been developed.

The effect of the doping on the growth and superconducting properties of whiskers in the Bi–Sr–Ca–Cu–X–O system (where X = Na, B, Ga, and Pb, respectively), prepared by heating a glassy melt-quenched plate in flowing oxygen, is reported. The thermal behavior of the glassy samples (studied by DTA, XRD, and SEM techniques) was found to be dependent on the dopant as well as on its concentration. The Bi2Sr2CaCu2Ox (2212 phase) whiskers were grown only from the Ga-doped system annealed at 855 °C. The dependence of the mechanism of the whiskers' growth on the dopant is also discussed.

The synthesis of Bi2−xPbxSr2Ca2Cu3O10 (Bi2223) powders from a freeze dried nitrate precursor is reported here. We examine the composition and morphology of the precursor material, describe the chemistry and kinetics of product formation, and evaluate the phase composition and superconducting properties of the products. A nitrate solution containing the appropriate ratio of cations was rapidly frozen and then freeze dried at low temperatures to form an atomic mixture of the component salts. The thermal processing of the freeze dried material consisted of three steps: (i) dehydration, (ii) denitration, and (iii) solid state reaction to form the Bi2223 superconducting product. Calcium-substituted bismuthates and strontium-substituted calcium cuprate, not Bi2201, are the intermediates between the nitrates and the superconducting products. These highly disordered phases rapidly transform into Bi2212 or Bi2223 at higher temperatures (≍790 °C). The kinetics of product formation was studied using XRD analysis and magnetic susceptibility. The kinetics were shown to follow the nucleation and growth mechanism. Bi2223 formed after only 30 min at a few degrees below the melting point, and after 37 h Bi2223 products exhibited excellent phase composition and magnetic susceptibility characteristics.

The microstructure of gas-atomized Al-20 wt. % Si-1 wt. % Ni powders was investigated by electron microscopy. Primary Si crystals about 2 μm in size are homogeneously distributed in the Al matrix. Eutectic Si crystals about 50 nm in size are precipitated with the definite crystallographic relationship of 〈110〉Si ‖ 〈110〉Al. Most of the interfaces between Al and Si are semicoherently bonded with close-packed planes of {111}Si and {111}Al. The special crystallographic relationship and interfaces are interpreted by matching between Si and Al lattice spacings.

The hardness, H, and rate sensitivity of the hardness, m = ∂ ln H/∂ ln ∊eff|xp, where ∊eff is an effective strain rate and xp the plastic depth, are measured in molybdenum at room and low temperature (160 and 170 K) using as-received and annealed specimens. Based on these measurements it is found that H separates into two components: one depending on indentation rate and temperature, and the other depending on the starting state of the material. An activation volume is defined, v∗ = 9kT/mH, which falls within the range of values derived from other experimental techniques. The values of m obtained from indentation creep, indentation load relaxation, and indentation rate-change experiments agree closely with each other provided a consistent analysis is used. The results of these experiments suggest that the rate- and temperature-dependence of the hardness can be used to discriminate between strengthening mechanisms at low temperature.

PAES (Positron Annihilation induced Auger Electron Spectroscopy) intensities from ultrathin Au films deposited at 198 K on Cu(100) were measured as a function of temperature (from 198 K to 348 K) for three different Au coverages. Intermixing of Au and Cu atoms with the increase of temperature was directly monitored. The measurements indicated that the intermixing was not reversible as a function of temperature. EAES (Electron induced Auger Electron Spectroscopy) results were compared with PAES results for each experiment, and the comparison showed the feasibility of PAES over EAES for the study of surface alloy formation as a function of temperature.

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350–450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.

Dielectric polarizabilities for most of the ions in known perovskites scale with the ionic volume and the valence. These ionic dielectric polarizabilities and the ion additivity rule have been used to calculate molecular dielectric polarizabilities for perovskite substrate materials used for high-temperature superconductors. Using the ion additivity rule to predict possible low permittivity compositions seems to suggest that the constraints of the perovskite structure and stoichiometry, lattice match to high-temperature superconductors, and congruent melting required for bulk growth limit the compositions to ones unlikely to be superior to the currently available materials. The most limiting factor on the relative permittivity of the perovskites is probably the close-packed nature and lack of voids in the structure. However, in nonferroelectric perovskites, the polarizabilities derived from relative permittivity data using the Clausius-Mossotti relation are significantly less than the calculated values, with deviations that correlate with degree of cation compression. Use of cation compression to reduce the polarizability shows some promise for improving dielectric constants.

Ferroelectric BaTiO3 thin films were deposited on Si by rf magnetron sputtering. A conductive oxide, RuO2, was used as the bottom electrode of the capacitors. The performance of the thin film capacitors was found to be a strong function of the surface and interface properties between ferroelectric BaTiO3 and the bottom electrode. A suitable capacitor configuration must be used to preserve the bottom electrode, to enhance the dielectric constant, and to reduce the leakage current density of the films. BaTiO3 thin film on the RuO2/Si substrate, where the BaTiO3 thin film has a bilayer structure of polycrystalline on microcrystalline, showed a dielectric constant of 125 at a frequency of 1 MHz, leakage current density of 10−6 A/cm2 at a field intensity of 2.5 × 105 V/cm, and a breakdown voltage above 106 V/cm.

By depositing thin films under conditions where intensity oscillations are observed in RHEED (reflection high-energy electron diffraction) spots, unit cell level multilayers of SrTiO3/BaTiO3 structures have been grown by pulsed laser ablation. High resolution TEM (transmission electron microscopy) and STEM (scanning transmission electron microscopy) observations of the deposits show that epitaxial multilayers with layer thicknesses of 1, 2, 4, 8, and 16 unit cells can be grown on [100] orientation SrTiO3 substrates. The superlattices show partial intermixing of the Sr and Ba for layer thicknesses less than 8 unit cells, but incomplete intermixing occurs even when the layers are only a single unit cell thick. From observations of the degree of intermixing at different depths in the deposit, it was determined that most of the intermixing takes place during deposition and not during subsequent annealing of the deposit. The 16 and 8 unit cell thick BaTiO3 layers were found to be tetragonal with the c-axis of the layers oriented normal to the substrate but with the a-axis strained to coherently match the SrTiO3 layers.

Spatially resolved electron energy-loss data have been recorded at the interface between niobium and sapphire (α-Al2O3), a model metal/ceramic couple. The spatial-difference technique is used to extract interface specific components of the energy-loss near-edge structure (ELNES), which are dependent on the chemistry and bonding across the interface. Multiple scattering calculations of aluminum, oxygen, and niobium clusters were performed to simulate the measured Al L2,3 ELNES. Two samples fabricated by different techniques were examined. The first interface was made by diffusion bonding pure crystals. Its interface spectrum is identified with tetrahedral coordination of the Al ions at the interface. The calculations match the experimental edge structures, supporting the notion of aluminum to niobium metal bonding and concurring with a structural model in which the basal plane of sapphire at the interface is terminated by a full monolayer (i.e., 67% excess) of aluminum. The second sample was produced by molecular beam epitaxy. The spectrum of this interface is consistent with an atomistic structure in which the interfacial basal plane of sapphire is terminated by oxygen. An unoccupied band of states within the band gap of Al2O3 is observed, signifying chemical bonding between metal and ceramic.

The electrochemical codeposition of In and Sb from a novel low temperature molten salt electrolyte is reported. The melt, which consists of InCl3 and 1-methyl-3-ethylimidazolium chloride, allows the codeposition to be accomplished at 45 °C. XPS shows that InSb can be deposited from this system. Electrochemical experiments are provided along with an interpretation that draws on the importance of In(I) species in the melt.

A theoretical model of the combustion synthesis process has been developed. In particular, a set of nonlinear and interrelated partial differential equations is given that accounts for all of the relevant physical and chemical processes that occur during the combustion synthesis process. The appropriate conservation equations for thermal energy, mass, and momentum densities are correctly described—for each phase at each point in the sample—at all times during the process. In addition, details of the necessary interphase transfer terms are expressed in a number of constitutive relationships, in which the dependence of an independent variable upon its dependent variable(s) is given explicitly. In doing so, microstructural details are accounted for, derived primarily from percolation concepts as applied to disordered porous media. All assumptions that are incorporated into the theoretical model have been tabulated in detail. This theoretical model establishes an approach to the development of a sound, quantitative, and fundamental understanding of the combustion synthesis process, particularly with respect to the processing-microstructure-properties relationship. It also provides a point of departure for conducting detailed, quantitative computer experiments of the combustion synthesis process.