MgAl2O4 films have been grown epitaxially on both Si(100) and MgO(100) by a novel single source metal-organic chemical vapor deposition (MOCVD) process. A single molecular source reagent [magnesium dialuminum isopropoxide, MgAl2(OC3H7)8] having the desired Mg: Al ratio was dissolved in a liquid solution and flash-vaporized into the reactor. Both thermal and plasma-enhanced MOCVD were used to grow epitaxial MgAl2O4 thin films. The Mg: Al ratio in the deposited films was the same as that of the starting compound (Mg: Al = 1:2) over a wide range of deposition conditions. The deposition temperature required for the formation of crystalline spinel was found to be significantly reduced and crystallinity was much improved on Si by using a remote plasma-enhanced MOCVD process. The epitaxial nature of the MgAl2O4 films was established by x-ray pole figure analysis.

Due to the highly anisotropic properties of BSCCO superconductors, the bulk properties of these materials can be greatly affected by preferential orientation. Substantial c-axis orientation normal to the desired direction of current flow has been demonstrated by centrifugally slip casting lead-doped BSCCO-2223. The strong preferred orientation developed in the centrifugally slip-cast material demonstrates high critical current potential.

The microhardness of monoclinic ZrO2 single-crystals was measured in different environments: air, water, and toluene. An indentation creep process at room temperature was observed for the measurements in moist media pointing for a water-activated plastic relaxation mechanism. This effect is discussed employing the models previously proposed to explain similar behaviors in ZrO2 and other nonmetallic materials. A possible correlation with the conditions for the nucleation in phase transitions is proposed.

Using high reactor pressures (>1 bar) and a unique rate control mechanism, three fibers were recently obtained by laser assisted chemical vapor deposition (LCVD) having elemental (i.e., boron, carbon, and silicon) compositions, small diameters (>9 μm), and surprisingly high growth rates (0.3–1.1 mm/s). By reacting silane and ammonia at high pressures (>1 bar) near the focus of a Nd-YAG laser beam, we have now obtained the first LCVD fibers with binary (i.e., silicon-nitrogen and silicon nitride) compositions having small diameters and high growth rates (0.34–0.74 mm/s). These fibers were amorphous.

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.

A Ni-P solid-solution phase was obtained by quenching from the melt under a pressure of 4.5 GPa. It was considered as a metastable high-pressure phase. Metastable phases with the same composition as the melt, such as supersaturated solid solutions and amorphous phases, are easily prepared using a high pressure quenching method.

The effect of uv irradiation on the material properties of AlN containing low oxygen content (<0.3 wt. %) has been investigated. Upon irradiation with a 150 W Hg-Xe arc lamp, increases in dielectric loss and thermal conductivity drops were observed. Changes in the optical properties, including formation of an absorption band at 650 nm, and photodarkening were also observed. All samples were characterized for trace impurities including carbon, calcium, and oxygen. The magnitude of the uv-induced drops in dielectric loss and the absorption at 650 nm of samples tested were found to depend on the presence of trace levels of residual carbon. UV-induced increases in dielectric loss show an inverse relationship, and formation of an absorption band shows a direct relationship to carbon content.

Silicon nitride films are grown by plasma enhanced chemical vapor deposition from tetrakis(dimethylamido)silicon, Si(NMe2)4, and ammonia precursors at substrate temperatures of 200-400 °C. Backscattering spectrometry shows that the films are close to stoichiometric. Depth profiling by Auger electron spectroscopy shows uniform composition and no oxygen or carbon contamination in the bulk. The films are featureless by scanning electron microscopy under 100,000X magnification.

Containerless processing of YBa2Cu3O7−δ was performed using an aero-acoustic levitation technique. Upon solidification from the liquid, spheres of size 2.5 mm diameter undercooled and recalesced, forming tetragonal YBa2Cu3O7−δ directly from the melt. Subsequent to solidification processing, these samples were annealed to single phase YBa2Cu3O7−δ with orthorhombic symmetry as indicated by powder XRD, SQUID magnetometer measurements indicate a sharp superconducting transition at approximately 85 K. Magnetic Jc values, calculated using the Bean critical state model, indicate that the spheres can carry critical current densities on the order of 104 A cm−2. Microstructural characterization has been performed on both the as-solidified and annealed spheres.

Microtubes of ZnO have been produced using sputter coating and a fugitive phase technique. ZnO was sputtered onto polyester fibers by dc magnetron sputtering, and the polyester fiber fugitive phase was subsequently burned out by annealing in air or oxygen. Tubes with an inside diameter of 23 μm and a length of 3 cm were obtained. The 3 to 6 μm thick walls of the tubes exhibited a [002] radial texture.

The microstructures and mechanical properties of single phase and multiphase alloys are reported for Al-rich intermetallic alloys containing up to 45 at. % Ti and as much as 68 at. % Cr. Among the individual phases formed in these alloys, TiAl and tau (Al67Cr8Ti25) had both the lowest hardnesses and the greatest resistance to cracking. Additionally, the presence of these two phases in multiphase alloys improved mechanical properties.

C60 films were deposited on a variety of substrates by thermal evaporation. The presence of C60 in the films was confirmed by Transmission Electron Microscopy and Raman spectroscopic analysis. The C60 films exhibited an average friction coefficient of 0.4–0.5. The films were irradiated with 2 MeV Ag+ and B+ ions at various doses. High energy ion bombardment created damage that resulted in partly crystalline to amorphous films, dependent on the mass and dose of ions. The amorphous films showed a friction coefficient of <0.1. Partly crystalline films showed a friction coefficient at the same level as that of unirradiated films.

Stabilization of zirconia into cubic phase is achieved by partly substituting Zr4+ with Mn4+ ions (5–30 mole %) via hydroxide gel formation and subsequent calcination at 773 K and is supported by XRD and IR data. A linear correlation between the lattice parameter and the Mn content confirms the incorporation of Mn into ZrO2. The XPS and TPR results provide some evidence for the presence of Mn4+ ions in these samples which have a surface area of about 100 m2 g-1 and are stable in the cubic phase up to 973 K. On reduction above 973 K, the cubic phase is stabilized probably by Mn2+ ions.

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 importance of the interactions between alloy atoms and topological defects for the thermodynamic properties of nanostructured alloys is pointed out. The McLean model for grain boundary segregation is extended to yield an expression for the total Gibbs free energy of an alloy polycrystal. This provides a simple conceptual basis for a qualitative discussion of the thermodynamic properties of nanocrystalline alloys. It is demonstrated that certain alloy poly- or nanocrystals may reach a metastable state, where the alloy is stable with respect to variation of its total grain boundary area.

Amorphous aluminosilicate gel powders have been subjected to carbothermal reduction and nitridation reaction at high temperature (1673 K). The influence of Al2O3 content in the gel powder on the nature and structure of the product phases has been examined. Between 5% and 9% Al2O3 in the gel powder, it is found that only β-SiAION is formed as the product of CTR/N reaction.

Self-limited growth of InAs at 480 °C is achieved by a rotating substrate method with a specially designed susceptor. The residual precursors and the boundary layer are removed by the mechanical shear-off. Prevention of the precursor carryover and the gas-phase decomposition are thought to result in the self-limited growth of InAs at temperatures as high as 480 °C.

YBa2Cu3O7−x (YBCO) superconducting thin films that show no x-ray diffraction peaks due to any other non-superconducting phases have been synthesized by annealing Y-Ba-Cu-O amorphous precursors at 750 °C. The Y-Ba-Cu-O precursors have been fabricated by oxidizing Y-Ba-Cu metallic precursors coevaporated from Y, Ba, and Cu metallic sources under ultrahigh vacuum conditions. Crystallization behavior from the Y-Ba-Cu-O precursor to YBCO films drastically depends on an oxidation temperature for the Y-Ba-Cu metallic precursor. YBCO thin film synthesized from the precursor oxidized at an optimum temperature shows a zero resistance temperature of over 80 K and a very smooth surface.

The effect of Ga doping on the grain boundary properties of a ZnO varistor has been presented in this note. Within the range of doping level studied, it is shown that Ga acts as a donor at the grain boundary and behaves similar to that of Al.1 The grain boundary doping behavior of both Ga and Al, when acting as donors, can therefore be represented by the same defect model.

Oriented diamond films have been nucleated on single crystal nickel substrates seeded with non-diamond carbon and annealed at high temperatures in atomic hydrogen. The non-diamond carbon seeds included graphite powders, fullerene (60) powders, and gaseous carbon species. It was found that these different non-diamond carbon powders or species were effective in the enhancement of oriented nucleation of diamond. The morphologies of diamond films were similar regardless of the types of carbon used, suggesting a common nucleation mechanism involved. Based on the experimental observations, a revised model was developed for the oriented nucleation of diamond on Ni.