Highly oriented diamond films were grown on single-crystal silicon substrates. Textured films were first nucleated by a two-step process that involved the conversion of the silicon surface to an epitaxial SiC layer, followed by bias-enhanced nucleation. The nucleation stage, which produced a partially oriented diamond film, was immediately followed by a (100) textured growth process, thus resulting in a film surface where approximately 100% of the grains are epitaxially oriented relative to the silicon substrate. The diamond films were characterized by both SEM and Raman spectroscopy. Structural defects in the film are discussed in the context of their potential effect on the electrical characteristics of the resulting film.

70Ge and 74Ge isotopes were successfully separated from natural Ge and zone purified. Several highly enriched, high purity 70Ge and 74Ge single crystals were grown by the vertical Bridgman method. The growth system was designed for reliable growth of low dislocation density, high purity Ge single crystals of very small weight (∼4 g). A 70Ge and a 74Ge crystal were selected for complete characterization. In spite of the large surface to volume ratio of these ingots, both 70Ge and 74Ge crystals contain low electrically active chemical net-impurity concentrations of ∼2 × 1012 cm−3, which is two orders of magnitude better than that of 74Ge crystals previously grown by two different groups.1,2 Isotopic enrichment of the 70Ge and the 74Ge crystals is 96.3% and 96.8%, respectively. The residual donors and acceptors present in both crystals were identified as phosphorus and copper, respectively. In addition, less than 1011 cm−3 gallium, aluminum, and indium were found in the 70Ge crystal.

The solubility of Fe in CdSe crystal has been studied in detail in the past. Using powder diffraction and atomic absorption spectroscopy, it was concluded that the upper limit for the solubility of iron in CdSe is 12–15%, and the actual Fe concentration in a solid solution agrees with the nominal Fe concentration (calculated from the concentration of the reactants). In the present study this question is re-examined using techniques that probe the average properties of the solid solution, such as x-ray diffraction, and techniques that probe the local structure and composition of the solid solution on the micron scale, such as energy and wavelength x-ray dispersive microprobe analysis. It is shown that the solubility of Fe in the CdSe matrix is appreciably smaller than the nominal value, and that microsegregation is obtained at a much lower Fe concentration than previously concluded. The immiscibility of Fe in this matrix is consistent with the large deviation of the lattice constants from Vegard's law. It is attributed to the large strain exerted on the lattice upon substitution of Cd by the much smaller Fe ion.

Polycrystalline tungsten nitride thin films were grown by low pressure metallo-organic chemical vapor deposition (MOCVD) using (tBuN)2W(NHtBu)2 as the single-source precursor. Deposition of uniform thin films on glass and silicon substrates was carried out at temperatures 723–923 K in a cold-wall reactor, while the precursor was vaporized at 333–363 K. The growth rates were 2–10 nm/min depending on the condition employed. Bulk elemental composition of the thin films, studied by wavelength dispersive spectroscopy (WDS), is best described as WNx (x = 0.7–1.8). The N/W ratio decreased with increasing temperature of deposition. X-ray diffraction (XRD) studies showed that the films have cubic structures with the lattice parameter a = 0.414–0.418 nm. The lattice parameter decreased with decreasing N/W ratio. Stoichiometric WN thin films showed an average lattice parameter a of 0.4154 nm. X-ray photoelectron spectroscopy (XPS) showed that binding energies of the W4f7/2, W4f5/2, and N1s electrons were 33.0, 35.0, and 397.3 eV, respectively. Elemental distribution within the films, studied by secondary ion mass spectroscopy (SIMS) and Auger spectroscopy depth profilings, was uniform. The SIMS depth profiling also indicated that C and O concentrations were low in the film. Volatile products trapped at 77 K were analyzed by gas chromatography–mass spectroscopy (GC–MS) and nuclear magnetic resonance (NMR). Isobutylene, acetonitrile, hydrogen cyanide, and ammonia were detected in the condensable mixtures. Possible reaction pathways were proposed to speculate the origin of these molecules.

ZrO2 thin films were deposited at 1 atm on Si substrates by oxidation-assisted thermal decomposition of zirconium-trifluoroacetylacetonate in the temperature range of 300–615 °C. Above a deposition temperature of 400 °C, the deposited thin films have a columnar grain structure, where each grain is perpendicular to the substrate surface with a c-axis preferred crystallographic orientation, and have poor electrical characteristics as a dielectric thin film. But the thin film deposited at 350 °C has a fine equiaxed microcrystalline structure and has superior electrical characteristics of a breakdown field of 1 MV/cm and a relative dielectric constant of 27.

The unusual sigmoidal behavior between electrical resistivity and inverse temperature in polycrystalline porous SnO2 was intensively investigated by detecting the localized traps formed at the interparticle through the measurement of Isothermal Capacitance Transient Spectroscopy. A trap of 1.0 eV was evaluated at a higher temperature range of 460–500 °C, and 0.6 eV trap at a lower temperature range 200–280 °C. It seems that the trap of 1.0 eV originates from O2− and 0.6 eV from O− defect center. Time constants which were determined at the peak position of ICTS spectra, S(t), were increased with the increase of temperature at the intermediate temperature range, indicative of the competition among various kinds of traps. The active competition among various traps is one of the causes that result in prominent gas sensitivity in polycrystalline porous SnO2.

Dy2O3 layers have been grown on SrTiO3 by molecular beam epitaxy. X-ray and electron diffraction patterns clearly show that Dy2O3 grows epitaxially on SrTiO3 with {100} planes parallel to the substrate surface. Transmission electron microscopy reveals that the Dy2O3 film breaks up into small domains (10–40 nm). This leads to the formation of terraces which limits the structural perfection of thin overgrown DyBa2Cu3O7 by introducing steps and small misorientations (within 3°). The resulting surface corrugation does not preclude the growth of epitaxial c-axis DyBa2Cu3O7 films with a Tc0 of 86 K. Crystallographic analysis and image calculations show that the domain growth of Dy2O3 is associated with the formation of 90° rotation twins.

We explain observed Hf-site interchange in LiNbO3 and LiTaO3 at high temperatures using solid-state defect chemistry reactions. The model takes into account fully the effects of nonstoichiometry on the ferroelectric-to-paraelectric phase transition. Specifically, we use this model to interpret the temperature dependence of the Hf-site interchange that we measured using perturbed-angular-correlation (PAC) spectroscopy. In this context, the site interchange is an equilibrium, thermodynamic process that involves the partitioning of Hf ions between Li and group-V (Nb and Ta) sites. The Hf ions replace group-V ions by pushing them from their normal sites to the Li sublattice. Based on the temperature dependence of the site occupancy, this reaction requires approximately 2.2 to 2.3 eV.

Ceramic materials with chemical compositions of CaO–X mole % TiO2, where X ranges from 3 to 40, have been prepared for the evaluation of microstructures, mechanical properties, thermal shock resistance, resistance to hydration in air, and resistance to corrosion in molten salt saturated with calcium. When the TiO2 content is less than 40.3 mole %, the CaO forms two-phase microstructures consisting of CaO and Ca3Ti2O7, and the composition CaO−40.3 mole % TiO2 corresponds to the (single-phase) compound Ca3Ti2O7. The data on mechanical properties suggest that the single-phase material has better flexural strength and fracture toughness than do the two-phase materials. It is also demonstrated that the stabilizing effect of TiO2 on CaO imparts resistance to atmospheric hydration. Both scanning electron microscopy and energy-dispersive x-ray analysis of the specimens exposed to molten CaCl2−20 mole % CaF2 saturated with calcium at 900 °C show that corrosion resistance increases with an increase in TiO2 content, but that corrosion does occur in all materials. On the basis of experimental observations and thermodynamic considerations, the degradation of Ca3Ti2O7 is shown to be associated with the reduction of Ca3Ti2O7 by calcium to form CaO and metallic titanium followed by the dissolution of the reaction product CaO in the molten salt.

Lanthanum sulfide (La2S3) exists in three different allotropic forms in the crystalline state. The low-temperature orthorhombic phase (α) transforms to the intermediate tetragonal phase (β) which further undergoes transformation to the high-temperature cubic phase (γ). The intermediate tetragonal phase (β) is an oxysulfide with possible use as a phosphor, and the cubic phase (γ) of La2S3 shows potential for application as a far IR (8–14 μm) window material. We report metal-organic synthesis routes for the preparation of the β- and γ-phases of La2S3 by processing modifications and choice of precursor chemistry. The alkoxide-derived precursors and the transformed sulfide powders were characterized for morphology, microstructure, and thermal stability. Phase evolution studies were also conducted, and the results are discussed in the context of formation of the β- and γ-phases. Results of densification, microstructure, and infrared transmission characteristics are also presented.

Vickers indentation sites in ceramics have been examined after specimen failure from median/radial indentation cracks. Evolution of a new cracking pattern of “ortho-lateral” cracks, originating at the intact corners of the Vickers indentation and running orthogonal to the classic-lateral cracks and parallel to the new fracture surface, has been observed. In some instances postfailure extension of the classic-lateral cracks toward the surface was also observed. Enhanced residual tensile stress from relaxation of constraints on the indentation-plastic cavity by the generation of a fracture surface is postulated to drive the subsidiary cracking. A simple qualitative model to explain this phenomenon is presented. Possible implications of such postfailure subsidiary cracking on residual-stress-driven flaws, postmortem fractography, and wear in ceramics are discussed.

Fine particles of mixed oxides having the composition MgxFe2−2xO3−2x (x between 0 and 1.0) were prepared via the sol-gel supercritical drying route (aerogels). Samples were then postprocessed by heating in air at 773 K and 1073 K. The structure and chemistry of the samples were deduced through x-ray diffraction, thermal gravimetric and differential thermal analysis, infrared, and specular UV-visible measurements. Surface areas were measured by the BET method. The volume saturation magnetization and particle volume distribution of MgFe2O4 samples were deduced from vibrating sample magnetometer measurements. The samples with x = 0 and x = 0.5 were well-crystallized α–Fe2O3 (hematite) and MgFe2O4 (magnesioferrite), respectively. Samples with 0 < x < 0.5 consisted of disordered lacunar spinels containing an excess of Fe3+ with respect to the spinel stoichiometry and a small amount of Fe2+. Samples heated above 773 K showed progressive segregation of α–Fe2O3. The sample with x = 0.66 was a mixture of a spinel phase and a hydrotalcite-like mixed Fe–Mg hydroxy compound containing methoxy and acetate ions. By heating in air, a monophasic Mg-excess spinel-type structure was obtained. The samples with 0.66 < x < 0.86 were mixtures of a spinel-type phase and another mixed Mg–Fe compound. When heated in air, the samples gave a mixture of MgO (probably containing Fe ions) and MgFe2O4. The saturation magnetization of MgFe2O4 samples is comparable to those previously reported, with the as-produced sample having a mean particle radius of 5.5 nm.

MoSi2-based composites have been synthesized through the mechanical alloying (MA) of elemental molybdenum and silicon powders with and without carbon additions. The interplay between the phase formation sequence in the powders and the microstructural evolution in the consolidated samples is described. It is shown that the glassy SiO2 phase characteristic of conventional powder processed MoSi2 can be effectively eliminated by combining mechanical alloying, carbon additions, and an in situ carbothermal reduction reaction. Using this approach, composites consisting of uniformly distributed micron-size SiC in an MoSi2 matrix can be formed. The effect of important processing variables such as the extent of carbon additions, extraneous iron pickup during MA, partial pressures of oxygen, consolidation temperatures, and consolidation atmospheres is discussed based on the evidence obtained from DTA, TGA, TEM, and XRD.

Conductivity relaxation spectra of sol-gel-derived glasses in the system Li2O (1 – x) SiO2, with x varying from 0.15 to 0.25, have been analyzed using a heterogeneous conductor model. The latter comprises diagonal layers of phases, one of them being rich in alkali ions and the other deficient in the same. Satisfactory agreement between the experimental data and the theoretical curves has been obtained over the frequency range 100 Hz to 1 MHz. The Kohlrausch–Williams–Watts (KWW) exponent, β, has been calculated from the conductivity spectra for all the glasses. The sol-gel-derived glasses have β values smaller than those obtained in the case of the corresponding melt-quenched ones. The β value is found to be correlated to the conductivity fluctuation in the alkali-rich phase.

Vanadium nitride has been synthesized with a surface area of 120 m2 g−1 by temperature programmed nitridation of a foam-like vanadium oxide (35 m2 g−1), precipitated from vanadate solutions. The nitridation reaction was established to be topotactic and pseudomorphous by x-ray powder diffraction and scanning electron microscopy. The crystallographic relationship between the nitride and oxide was {200}//{001}. The effect of precursor geometry on the product size and shape was investigated by employing vanadium oxide solids of different morphologies.

In the ordinary application of the time-lag method to the measurement of the diffusion coefficient of a gas passing through a plane sheet of an inert solid, the gas is pressurized on one side of the sheet and evacuated on the other. After decay of transients, the cumulative amount, Q(t), of gas diffused through the sheet in time, t, assumes the “time-lag” form, Q(t) = A(t – L). Measurements of the slope, A, and the intercept, L, can be used to determine the diffusion coefficient and the solubility of the gas in the solid. We have rederived this law for the case of a solid that is actively evolving this same gas at an arbitrary rate and have used it to predict the rate of outgassing of the solid upon standing. Practical applications of the theory include radioactive decay of minerals, rejection of plasticizers by plastics, and the decomposition of solid rocket propellants.