Geometrical modeling of the B2 structure indicates that the tetrahedral interstitial site is always the largest both before and after an a/2〈111〉 translation on {110}, such as occurs during the slip of a partial dislocation in some B2 compounds. The tetrahedral site within the APB which trails a gliding a/2〈111〉 dislocation is larger than in the unslipped lattice, suggesting that interstitial atoms will segregate there. Also, some interstitial sites in a B2 lattice are larger than those in a bcc lattice of the same lattice parameter, suggesting that interstitials may have greater solubility in B2 compounds.

Solid solutions of aluminum nitride (AlN) and silicon carbide (SiC), the only intermediate phases in their respective binary systems, have been grown at 1050 °C on α(6H)-SiC(0001) substrates cut 3–4° off-axis toward [11$\overline 1$0] using plasma-assisted, gas-source molecular beam epitaxy. A film having the approximate composition of (AlN)0.3(SiC)0.7, as determined by Auger spectrometry, was selected for additional study and is the focus of this note. High resolution transmission electron microscopy (HRTEM) revealed that the film was monocrystalline with the wurtzite (2H) crystal structure.

In recent experiments it has been shown that the yield stress of polycrystalline thin films depends separately on the film thickness and the grain size. It was also shown that the grain size dependence varies as the reciprocal of the grain size. In this paper an analysis is presented which leads to these results and provides a more detailed understanding of the origins of the observed behavior.

Recent morphological studies of vapor-deposited diamond indicate (1) that growth on the diamond {100} surface is mediated by steps and (2) that some defects cause rapid initiation of new layers, resulting in characteristic pyramids with edges parallel to surface 〈110〉 directions. If growth on the diamond {100} surface does indeed occur at steps, knowledge of their atomic structure is essential to an understanding of diamond growth. We reexamine results of a recent STM study of homoepitaxial diamond films and suggest that the surfaces on which growth occurs consist of regularly spaced double height steps separated by integral numbers of dimer rows running parallel to the step edges.

The partial molar entropy of solution of oxygen in YBa2Cu3Ox, δsO, has been computed using equilibrium data and the recently measured partial molar enthalpy of oxygen. While δhO is independent of oxygen content (6 < x < 7), δsO depends on x. The po2, T location of phase equilibrium between the 123 and 124 superconducting phases is calculated. The standard free energies of interactions of the superconducting phases with carbon dioxide (CO2) and water vapor (H2O) have been assessed. The free energies of carbonation of the fully oxidized 123 and 124 phases are −323 ± 22 kJ mol−1 and −291 ± 32 kJ mol−1, respectively. The free energies of hydration of the 123 and 124 are −397 ± 22 kJ mol−1 and −469 ± 32 kJ mol−1, respectively. These large exothermic values show that degradation of these superconductors at ambient conditions is thermodynamically favorable.

Dependence of the contents and the states of residual carbon in YBa2Cu3O7−x powders synthesized by the sol-gel method on heating conditions, and effects of residual carbon on the superconducting properties were investigated. The carbon content of the powder heated at 950 °C for 20 h was reduced to 0.02%. It has been found that a large number of carbonaceous materials in the starting materials that are used in the sol-gel method does not affect the carbon content of synthesized superconducting powders. The volume of diamagnetism was increased and the Tc,onset was raised as the carbon contents were reduced to 0.04%. These properties were further improved by O2–HIP treatment at 500 °C.

Highly oriented SnO2 thin films have been grown successfully from tetra-n-butyltin on heated glass substrates by a pneumatic spraying system. The effects of film growth rate and substrate temperature on the microstructures of the films were investigated by x-ray diffraction and scanning electron microscopy. The SnO2 films of preferentially oriented (110) crystal plane were grown under the optimum growth conditions.

Zirconia-toughened MgO was manufactured and examined by scanning and transmission electron microscopes. It was found that ZrO2 particles that are present on the MgO grain boundary limit the grain growth of MgO. The cooling rate has an effect on the ZrO2 phase in zirconia-toughened MgO fired in a cubic ZrO2–MgO field, but it does not have an effect on the ZrO2 phase in specimens fired in a tetragonal ZrO2–MgO field. Tetragonal ZrO2 was retained at room temperature in zirconia-toughened MgO.

The reaction between alumina and yttrium barium cuprate subjected to a melt-texturing heat treatment was studied. Microstructural examination of quenched, partially transformed samples revealed that at ∼1050 °C (which is above the incongruent melting temperature of YBa2Cu3O6+x) a reaction layer forms at the alumina interface. The reaction products were identified as Ba6Y2Al4O15 and a copper-rich liquid phase. On cooling below the peritectic temperature, aligned domains of YBa2Cu3O6+x (123) were observed to nucleate preferentially at the reaction layer. For samples of melt-textured 123 deliberately seeded with alumina particles, it was found that nucleation and growth of 123 occurred exclusively at the particles. A reaction sequence for the formation of the Ba6Y2Al4O15 is put forward, together with a discussion of the possible nucleation mechanisms for the 123.

The structures of two laser processed ternary intermetallic phases, Al16Ti6(Fe or Ni)7, have been studied by using electron diffraction and microscopy. A convergent beam electron diffraction (CBED) technique for structure determination is described based upon the principle of kinematic interpretation of large angle systematic reflections in CBED disks. The structure type of phases Al16Ti6(Fe or Ni)7 is characterized as the Mn23Th6(cF116)-type, the same as those of relevant phases Cu16Mg6Si7 and Al50Ti25Fe25 etc., by using the CBED technique. Various errors involved in the analyses are also discussed.

Strands of nanometer-sized silver particles have been grown at the glass-crystal interface of a suitable glass-ceramic system. The samples exhibit high values of dielectric constant of the order of 500 at temperatures in the range of 80 to 200 K. This is believed to arise due to the Gorkov–Eliashberg anomaly. Above 200 K, a dielectric dispersion is observed, which is explained on the basis of a diagonal-layer heterogeneous conductor model.

A molecular precursor barium zirconyl oxalate (BZO) was synthesized by exchange reaction between freshly generated water soluble sodium zirconyl oxalate and Ba-nitrate solutions at room temperature. The controlled pyrolysis of BZO in air at 800 °C/6 h resulted in the formation of single-phase cubic microcrystalline barium zirconate powder. These powders exhibit variable-shaped agglomerates with an average size ≍0.2 μm having a surface area ≍2.63 m2/gm.

We report the preparation of the quasicrystalline particle-dispersed Al base composite alloys for the first time. Icosahedral AlCuFe quasicrystalline (i-AlCuFe) particles were homogeneously dispersed in a crystalline Al matrix using a novel process which combined mechanical alloying and hot press techniques. Hardness of the composite alloy increases with increasing volume fraction of the i-AlCuFe particle, i.e., increases from 25 kg/mm2 for pure Al to about 120 kg/mm2 for a 25 vol. % i-AlCuFe particle dispersed alloy.

A seeding and multistep deposition process has been developed to nucleate and grow diamond films directly on Ni substrates in a hot filament chemical vapor deposition system. High quality diamond films have been deposited without graphite codeposition on both 〈100〉 oriented single-crystal Ni and polycrystalline Ni substrates. Both 〈100〉 and 〈111〉 oriented diamond nuclei have been observed depending upon the underlying substrate orientations. Molten metallic phases were found surrounding the diamond nuclei, and it is speculated that a liquid layer composed of nickel, carbon, and hydrogen also formed on the diamond surface during the growth. The oriented diamond is believed to have been achieved by the reorientation of seeded diamond particles into alignment with the Ni substrate due to interaction between the diamond and Ni lattices.

Mechanical alloying, a high-energy ball-milling technique, is now widely used for preparing alloy powders with metastable phases (crystalline or amorphous). The technique, however, may contaminate the powder with material eroded from the vial and milling media. We report on the analysis and effects of iron contamination on Al25Ge75 powders that we prepared by mechanically alloying mixtures of aluminum and germanium powders, using different mechanical alloying apparatuses.

Gd-1:2:3 films were synthesized from acetate precursors and spun-on to polycrystalline substrates of yttria-stabilized zirconia. The substrates were fired in air at 500 °C in between each applied coat. After applying 10–30 coats, they were crystallized by heating to 900 °C in Ar or O2 with or without the application of a 1 T magnetic field. The applied magnetic field was found to produce c-axis alignment for films <4 μm. Annealing in argon produced alignment, but the effect was less pronounced than annealing in oxygen. Substrates with films > 20 μm were not aligned for either environment.

Rapid solidification of the Zr3Al liquid alloy allows retention of the high temperature β–Zr solid solution with bcc structure. Mechanical grinding is shown to amorphize this metastable phase very easily. Calculations show that the retained bcc phase has a free energy above that of the amorphous phase. The density of bcc Zr3Al at room temperature is found to be 2% lower than that of its equilibrium L12-ordered fcc structure as determined from their respective lattice parameters. The bcc phase thus represents a 2% volume expansion with respect to the fcc structure.

Processing atmosphere and precursor effects on liquid phase formation were investigated in the BaO–CuO thin film system. Liquid phase was observed at a significantly lower temperature (∼620 °C) under N2 atmosphere with carboxylate solution precursors. In the processing of the YBCO oxide superconductors, formation of the liquid phase facilitated the decomposition of BaCO3 and crystallization of the YBCO grains. Larger grains and greater (00l) preferred orientation were also observed in the YBCO films prepared with the presence of the liquid phase.

Ba0.75Sr0.25TiO3 thin films have been deposited on single-crystal MgO substrates by pulsed laser deposition with the objective of forming ferroelectric films with a low Curie temperature. The films have been characterized by capacitance measurements and by transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectrometry (random and channeled). Films deposited with the substrate at 500 °C are polycrystalline, while those deposited at 650 °C are highly aligned and possibly epitaxial. The films are transparent in the visible region with an optical absorption edge at about 300 nm. Capacitance measurements on the polycrystalline films reveal a Curie transition at 283 K. The lowering of Curie temperature from the corresponding bulk sample is attributed to the films being under compression, as verified by Raman spectroscopy.

The synthesis of poly crystalline boron nitride films, with β-rhombohedral boron crystallites, was accomplished with BCl3–NH3–H2 in a tungsten hot filament chemical vapor deposition apparatus. Raman spectra and XRD results revealed that the crystal structure of the boron nitride films is similar to rhombohedral boron carbide B4C. The composition of these crystallites by XPS was found to give a ratio of boron to nitrogen of 3 : 1 . These results suggest that the boron nitride crystals obtained in this work are previously unreported compounds of a rhombohedral boron-rich boron nitride, analogous to boron carbide, B4C.