Recent work by the authors has been extended to demonstrate the formation of solid krypton in single-crystal magnesium oxide. The solid inclusions, which were formed by ion implantation at room temperature, have been identified by electron diffraction. The formation of solid noble gas inclusions at room temperature indicates that they were under a high pressure. This pressure was determined, based on the measured lattice parameter, to be 1.7 GPa.

A modified aerosol decomposition method was developed for producing sintered YBa2Cu3O7−δ (1-2-3) pellets having sharp superconducting transition Tc's at ∼90 K, fine grain sizes, and clean grain boundaries. This method used “precursor” powders, which were produced with an aerosol flow reactor at 550 °C, instead of in situ produced 1-2-3 powders commonly processed at 880–1000 °C. As determined by x-ray absorption and powder diffraction studies, the 1-2-3 powders produced by the modified route contain less cation disorders than the in situ produced powders. The disorder is speculated to be the cause of Tc-suppression and broadening. It cannot be removed unless high sintering temperatures were used (>950 °C), which resulted in large grains and impurities and cracks at grain boundaries.

Mechanochemical effects on the synthesis and pulverization process of the Ba2YCu3O7−y superconductor (abbreviated to BYCO) and BYCO–Ag composite were examined. Grinding of the precursor of BYCO promoted the homogeneous distribution of each element and subsequently the crystallinity of the precursors was decreased. The sintered body obtained by using the ground and calcined powder had complicated crystal phases consisting of the BYCO phase with secondary phases and resulted in the impairment of the superconducting transport current property. Grinding of crystallized BYCO powder decreased its grain size and crystallinity; the crystallinity was recovered by annealing. On the other hand, grinding contributed to the synthesis of the BYCO–Ag superconducting composite by minimizing the particle sizes and mixing of components. The BYCO–Ag composite so obtained displayed improvement of superconducting properties.

Grain growth in the GdBa2Cu3O7−δ high Tc superconductor was investigated. The composition Gd1.09Ba1.91Cu3O7−δ, within the solid solubility region, was selected for the present grain growth study. Differential thermal analysis did not reveal any thermal event except the incongruent melting point, which is indicative of the absence of a liquid second phase during grain growth. The final densities of isothermally annealed samples ranged from 91.3% to 93.7% of theoretical density. The microstructure observation showed a greater grain aspect ratio in this material than in YBa2Cu3O7−δ. The average grain aspect ratio was about 4.7. A very low grain growth exponent of 0.07 was found in the isothermal annealing temperature range from 965 °C to 1020 °C. By comparison with the results on the YBa2Cu3O7−δ system previously reported, it was concluded that the grain growth kinetics in these materials are strongly controlled by the anisotropy of the grain boundary energy. The activation energy of grain growth was calculated to be about 77 kJ/mole.

In a previous paper we studied vacancy diffusion in two high-angle twist grain boundaries in Cu, using the EAM. In this paper, we discuss vacancy diffusion along four additional twist grain boundaries, from 8.8–43.6°. Vacancy formation energies in all the possible sites were calculated (0.14–1.42 eV) and found to be directly related to the degree of coincidence with the neighboring crystal planes. The optimal migration paths were found to coincide with the screw dislocations which comprise the boundary. Vacancy migration energies were found to be low (0.02–0.52 eV). The activation energies for self-diffusion at the boundaries were found to be less than half of the bulk value, in general agreement with experiment. Calculated diffusion rates, δD, for medium-high angle twist grain boundaries were in reasonable agreement with experimental data for polycrystalline material. Diffusion rates were found to decrease with increasing twist angle, in contrast with two sets of conflicting experimental data.

Equations for the concentrations of vacancies and antisite defects in ordered alloys in thermodynamic equilibrium at and near stoichiometry have been derived as functions of defect energies and a Lagrangian parameter. While the resulting equations cannot be solved analytically and in general require iterative calculations, an approximation is given that permits simple numerical evaluation with just a minor loss of accuracy. Using defect energies obtained from an embedded-atom method calculation for Cu3Au, it is found that the adjustment for off-stoichiometric compositions is accounted for primarily by the creation of antisite defects rather than vacancies, and the vacancy concentration on Au sites is orders of magnitude less than that on Cu sites. There is a significant increase in the Au vacancy concentration but a slight decrease in the net vacancy content with increasing Cu fraction.

Although a NbAl3 alloy containing Cr, W, and Y has excellent oxidation resistance above 1440 K, it suffers from severe environmental attack during deformation at intermediate temperatures between 900 and 1100 K. Specimens tested in constant velocity and constant load direct compression tests showed varying degrees of degradation depending on environment (i.e., air or argon), surface finish, stress, and temperature. As a result, there were corresponding differences in mechanical behavior and in the observed microstructures. At high stresses and strain rates, specimens with as-machined surfaces were brittle at and below 1100 K when tested in air but showed fracture strains above 4% when deformed in argon. However, reproducible compressive ductility of 2–3% was attained on polished specimens tested in air. At intermediate stresses, the creep curves showed sudden and periodic increases in strain before the specimens failed catastrophically after about 80 h. Microstructural examination of these specimens revealed extensive oxidation within cracks. Constant load tests conducted at lower stresses below 100 MPa showed an apparent incubation period where the change in the length of the specimen was immeasurably small. Following the incubation period, which typically lasted between 10 and 110 h depending on stress, temperature, and surface condition, specimens increased significantly in length due to oxide growth. In this case, considerable oxide spalling occurred during the course of the test, often leading to a substantial decrease in the cross-sectional area of the specimen. Microstructural observations revealed extensive cracking in the oxide layer and in the matrix, where the cracks had originated at the oxide-metal interface. The effects of environment on the mechanical properties are rationalized with the help of a schematic environmental-deformation mechanism map.

The precipitation behavior, especially the early nucleation stages, of the industrial strip-cast Al3003 alloys was investigated by using transmission electron microscopy (TEM). An icosahedral quasicrystalline phase was found as secondary particles in these strip-cast alloys after heat treatment for a few seconds. Three different nucleation paths are proposed based on the TEM observations. They have the same origin, viz. (Mn, Fe)-containing Mackay icosahedra, and are governed by the composition of alloys, especially the Mn and Si content.

A new analysis of the deflection of square and rectangular membranes of varying aspect ratio under the influence of a uniform pressure is presented. The influence of residual stresses on the deflection of membranes is examined. Expressions have been developed that allow one to measure residual stresses and Young's moduli. By testing both square and rectangular membranes of the same film, it is possible to determine Poisson's ratio of the film. Using standard micromachining techniques, free-standing films of LPCVD silicon nitride were fabricated and tested as a model system. The deflection of the silicon nitride films as a function of film aspect ratio is very well predicted by the new analysis. Young's modulus of the silicon nitride films is 222 ± 3 GPa and Poisson's ratio is 0.28 ± 0.05. The residual stress varies between 120 and 150 MPa. Young's modulus and hardness of the films were also measured by means of nanoindentation, yielding values of 216 ± 10 GPa and 21.0 ± 0.9 GPa, respectively.

The reactive aspect of pulsed laser induced vaporization has been explored via synthesis of tungsten carbide films from an unreacted sintered mixture of the W–C system. Using low-angle x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), it is shown that stoichiometry and the extent of chemical compound formation in the deposited films depend upon the laser fluence. Two cases with energy density 20 J/cm2 and 40 J/cm2 are discussed and compared. An attempt has been made to illustrate the mechanism behind the reactive aspect of the deposition.

Diamond crystallites and thin films have been deposited onto polycrystalline aluminum substrates utilizing an electron cyclotron resonance microwave plasma-assisted chemical vapor deposition (ECR-PACVD) method. For all depositions, the substrates were biased to +40 V dc with respect to ground and their temperature was maintained at 500 °C. Similar deposits were obtained from two different feedgas systems at a total pressure of 1.33 Pa (10 mTorr). The first system consisted of a carbon monoxide (CO) and hydrogen (H2) mixture (CO:H2 = 20:80), and the second was a methane (CH4), oxygen (O2), and hydrogen (H2) mixture (CH4:O2:H2 = 21:10:69). The deposits were subsequently characterized by scanning electron microscopy, micro-Raman spectroscopy, and x-ray diffraction. The results of these analyses indicate that polycrystalline diamond was deposited onto aluminum substrates, as both individual crystallites and continuous films.

Several conductive structures which appeared to be usable as base electrodes in VLSI capacitors based on high dielectric materials have been annealed in oxygen at 650 °C. The studied structures were Pt/TiN, Pt/Ta, Au/TiN, Ru, and RuO2/Ru, prepared under a variety of conditions. The structures have been studied by Rutherford backscattering (RBS) and Auger Electron Spectroscopy (AES). It was found that none of the pure metals, Pt, Au, or Ru, can prevent the diffusion of oxygen to the underlying layer and its oxidation, thus causing a possible break in the electrical conduction path to the silicon substrate. Of the investigated materials, in the thickness range ≤ 110 nm only the RuO2/Ru couple preserved its electrical connectivity to the Si substrate and prevented diffusion of silicon to the surface of the electrode.

The linewidths of x-ray photoelectron spectra have been correlated with dislocation densities in a shock-damaged crystal of ammonium perchlorate (AP). A centimeter-size AP crystal was loaded at several sites with a diamond pyramid (Vickers) indenter, creating localized strain centers. The crystal was nonuniformly damaged by a rapidly decaying shock (peak pressure of 24.4 kbar at the entry surface), recovered intact, and cleaved through the indentations. The cleaved planes permitted interior analysis of the crystal by x-ray photoelectron spectroscopy (XPS) over a pattern of 1 mm by 1 mm areas. The linewidth of the Cl(2p3/2) spectra ranged from 1.70 eV for the region of greatest visible damage to 1.22 eV for the region of no visible damage, the same linewidth as that obtained for unshocked AP (control). The observed damage was compared to photographs in the literature of gamma-ray irradiated AP crystals, for which dislocation densities were reported. This provided an approximate correlation of dislocation density versus XPS linewidth. The correlation was refined by chemically etching and determining densities on another cleaved plane in the recovered crystal. By this technique, a ∼100X increase in dislocation density was determined for the region of greatest shock damage relative to an unshocked crystal. The strain fields associated with the impressions were found to enhance perchlorate decomposition when driven by shock. Distortion of the molecular lattice in the vicinity of a dislocation is the physical mechanism responsible for the broadening of the photoelectron lines. Ab initio calculations of the Cl(2p) energy level in the perchlorate anion predicted variations of 0.1 to 0.46 eV. Variations of this magnitude are sufficient to produce the observed linewidth broadening.

By the 90° laser light-scattering technique, it was possible to visualize ultrafine crystalline particles and to investigate their behavior in relation to the growth of KDP crystals in an aqueous solution. It was found that the scattered microparticles move randomly and exist inhomogeneously in the solution. The density of microparticles increases with increasing supersaturation. Whereas in the bulk solution, the movements of the particles are slow, as soon as they approach the crystal, they are rapidly sucked into the surface to within a certain distance, corresponding to the thickness of the diffusion boundary layer. On the growing surface, they move or shake themselves for a while, and eventually become invisible. The crystal growth rate increases proportionally with increasing the density of the microparticles and the supersaturation. The results suggest that they are subcritical crystalline particles which are formed in the KDP solution, and contribute to the crystallization of KDP from the aqueous solution.

This paper deals with the concept of microstructural engineering through donor and acceptor dopings within the grain and at the grain boundary of a polycrystalline semiconducting ceramic. These concepts are derived from an analysis of the “prebreakdown” and the “upturn” current-voltage characteristics of a ZnO varistor and from the construction of corresponding defect models as a function of donor and acceptor dopants at the grain and grain boundary. By using Li, Al, and Na as dopants, it is shown that the dopants can be grain or grain boundary specific in the ZnO microstructure and that they can act as donors, acceptors, or both, depending on the nature and concentration of dopants and their location on the host crystal lattice structure. In the case of the ZnO varistor, the grain and grain boundary properties can thus be tuned independently or concurrently by systematic engineering of the entire microstructure through defect dopings that are specific to the grain, grain boundary, or both. Following a detailed analysis of the defect models thus developed for the ZnO varistor, a set of ground rules are proposed for applying these concepts of donor and acceptor dopings at the grain and grain boundary to the general case of microstructural engineering in a polycrystalline semiconducting ceramic.

BaZrO3 and BaHfO3 modified polycrystalline BaTiO3 are candidate materials for transverse mode and pyroelectric charge coupled device (CCD) arrays. Addition of 3–4% barium zirconate and barium hafnate to barium titanate alters the temperature of phase transformations and with it, dielectric and pyroelectric properties. These additions create a temperature range close to room temperature where the pyroelectric coefficient is extremely high relative to the dielectric permittivity. These materials show a very high figure of merit for dielectric bolometer applications that is competitive with existing materials, while being relatively easy to prepare.

We have observed the formation of the hydrotalcite-like phase of lithium dialuminate, LiAl2(OH)6OH · 2H2O, and also the carbonate analog, by the oxidation of aluminum sheet and also aluminum powder in aqueous lithium hydroxide or lithium carbonate solutions. A secondary phase, bayerite, was also observed following the oxidation process, except when the aluminum was treated with lithium oxalate solutions where it is the principal phase. Results have been obtained for the time required to form a passivating film to hydrogen formation as a function of temperature and oxidizing solution. Grazing incidence x-ray diffraction of aluminum sheet samples, combined with polycrystalline x-ray diffraction on similarly treated aluminum powder, were used to evaluate the formation of the films. Both transmission and reflectance infrared absorption spectra on powder and sheet samples were used to support the x-ray observations. Scanning and transmission electron microscopies show morphological differences between preparations, film thicknesses of 10–20 μm, and also film defects. Additional SIMS analysis determined the relative lithium and aluminum concentrations in the films, suggesting that a higher concentration of lithium occurs when lithium carbonate is present in the reacting solutions.

We conducted a series of hydrostatic and constant shear stress experiments at room temperature on three different sintering runs of unpoled, niobium-doped lead-zirconate-titanate ceramic (PZT 95/5–2Nb) in order to quantify the influence of shear stress on the displacive (possibly martensitic), first-order, rhombohedral → orthorhombic phase transformation. Inter- and intra-batch variations were detected, but some generalizations can be made. In hydrostatic compression at room temperature, the transformation began at approximately 260 MPa, and was usually incompletely reversed upon return to ambient conditions. Strains associated with the transformation were isotropic, both on the first and subsequent hydrostatic cycles. Results for the constant shear stress tests were very different. First, the confining pressure and mean stress at which the transition begins decreased systematically with increasing shear stress. Second, we observed that the rate of transformation decreased with increasing shear stress and the associated elastic shear strain. This result contrasts with the typical observation that shear stresses increase reaction and transformation kinetics. Third, strain was not isotropic during the transformation: axial strains were greater and lateral strains smaller than for the hydrostatic case, though volumetric strain behavior was comparable for the two types of tests. However, this effect does not appear to be an example of transformational plasticity: no additional unexpected strains accumulated during subsequent cycles through the transition under deviatoric loading. If subsequent hydrostatic cycles were performed on samples previously subjected to shear stress, strain anisotropy was again observed, indicating that the earlier superimposed shear stress produced a permanent mechanical anisotropy in the material. The mechanical anisotropy probably resulted from a crystallographic preferred orientation that developed during the transformation under shear stress. Finally, in a few experiments on specimens from one particular sintering run, volume strain was often completely recovered and sporadic evidence for a shape memory effect was observed.

The role of product evaporation during lead monoxide (PbO) powder generation by aerosol decomposition (spray pyrolysis) was investigated at various temperatures in a flow reactor. Particles consisting of phase pure litharge and a mixture of litharge and massicot were formed with the dominant phase changing from litharge to massicot as the pyrolysis temperature was increased. Scanning electron microscopy showed particles produced at lower temperatures had a lumpy surface morphology and at higher temperatures appeared to be solid, indicated by the faceted surfaces and a plate-like morphology. Evaporative losses of PbOx, to the reactor walls were observed due to the substantial vapor pressure of PbOx. A simple model was developed that accounts for particle evaporation and mass transfer of lead oxide vapor to the reactor walls. This model suggested that the loss of lead oxide to the reactor walls was limited by diffusional transport of lead oxide vapor to the reactor walls.

Isothermal and nonisothermal sintering behaviors of glass-filled ceramics are compared in this paper. Equations developed to describe the kinetics of shrinkage for both techniques can be readily used to interpret the experimental data. It is shown that the kinetics of linear shrinkage of powder compacts during isothermal and nonisothermal constant rate of heating are consistent and can be described by the viscous flow of glass.