Silicon-aluminum oxynitrides and/or aluminum nitride were prepared by the reduction-nitridation of kaolin in graphite crucibles under hydrogen/nitrogen flow at temperatures in the range 1100 °C–1450 °C. Almost pure β'-SiAION was obtained in less than 24 h at 1200 °C. At high temperatures (e.g., 1450 °C) and for long reaction times (e.g., 10 h), β'-SiAION is fully reduced to AlN. In most preparations, β'-SiAION is formed together with small amounts of AlN. However, the formation of AlN can be limited by using short reaction times and/or by adjusting the reducing power of the atmosphere, i.e., the N2/H2 ratio. Compared to the carboreduction of aluminosilicates which always yields mixtures, the present method leads to almost pure products under appropriate conditions. The temperature for the formation of β'-SiAION is at least 200 to 400 °C lower than the temperatures used for the carboreduction of aluminosilicates or sintering of powders, respectively. A gaseous species formed by the reaction of hydrogen with graphite is suspected to be responsible for the nitriding reduction of kaolinite.

Thin epitaxial films of β-SiC were grown by CVD on (100), (111), and (112) TiC substrates. TEM observations of the resulting interfaces revealed that island nucleation prevailed in the early stages of deposition for all three substrate orientations. Films grown on (111) and (112) TiC were monocrystalline, while SiC films deposited on (100) substrates were polycrystalline and not epitaxial, a phenomenon attributed to the poor match of atomic positions in SiC and TiC on their respective (100) planes. The (111) interface was abrupt and atomically flat, while the (112) interface exhibited {111} facets and steps. Simulated images of the stable (111) interface were calculated based on several possible atomic configurations, and the atomic structure of the interface was deduced from comparisons between the simulated images and phase-contrast TEM images.

The defects and crystallinity of as-grown and annealed TiCx (grown by the high-pressure float-zone) were examined by TEM and double crystal x-ray rocking curves. Three types of subboundaries and planar defects within subgrains were observed in as-grown TiCx. Subboundaries are classified by structure as (i) wide-extended, fault-like defects (WEFLD's), (ii) edge dislocation arrays, and (iii) dislocation networks. Planar defects were observed at dislocation nodes of subboundaries and also within subgrains; this is the first reported observation of planar defects within TiCx subgrains. The misorientation and/or density of subgrains in TiCx was reduced significantly by annealing at 2300 °C in contact with graphite.

Sols of titania were obtained by the sol-gel method and their size profile was followed by dynamical light scattering. In the early stages of the reaction an unstable behavior was detected. After this unstable regime the particle size reaches a steady state where the sols have a constant size while increasing in number. Once the sol concentration reaches its overlap value, the gelation regime takes place. For samples prepared in this way Raman spectra and x-ray diffractometry were used to characterize the kinetics of crystallization of the material.

The electrolysis treatment of the hydrothermal-electrochemical method has been modified so that it permits SrTiO3 thin films to be grown on Ti electrodes being oxidized anodically in Sr(OH)2 solutions far beyond a thickness limit of several tens of nanometers hitherto attained. The relation between the total current passed through the Ti anode and the amount of the resulting SrTiO3 film was analyzed on the basis of a reaction model that interprets the anodic current to be compensated with electrons generated partly by oxidation of Ti and partly by decomposition of H2O. Current efficiency for the film growth was estimated to be in the range from 0.8 to 3% depending on the Ti electrode potential.

Using x-ray and neutron diffraction data, the degree of order of the octahedral site cations has been determined for the perovskites Sr2AlNbO6 and Sr2AlTaO6, which have been prepared by several different methods and annealed at temperatures up to 1690 °C. The degree of order generally increases with increasing synthesis temperature. The amount of cation ordering is, therefore, primarily controlled by kinetic processes and not by thermodynamic equilibrium considerations. Increased order obtained with increased heating time confirms this general kinetic limitation on the degree of order. However, annealing Sr2AlNbO6 in the highest temperature region resulted in some decrease in order, presumably due to thermodynamic considerations. The cubic edge of both compounds decreases significantly with increasing order. Ordered domains are separated by antiphase boundaries which occur in high concentrations. The cubic cell edge within the ordered domains is significantly smaller than the overall cell edge when the concentration of antiphase boundaries is high. The antiphase boundaries cause significant lattice strain which generally decreases as the concentration of antiphase boundaries decreases. Results on other A2M3+M5+O6 systems are briefly presented.

A multilayer composite of an oxide superconductor and a compositional gradient layer composite of a ferrite chip component was prepared by the aerosol filtration method. Homogeneous, minute, and arbitrary control of the composition profile was possible for the multilayer composite of the Bi system superconductor. High controllability for designing the composition profile of the compositional gradient layer of nickel zinc ferrite was confirmed by EPMA analysis.

Thin films in the system (1 - x) PbTiO3−xLa2/3TiO3 were prepared by the sol-gel and dip-coating methods. Phases deposited in the films and the lattice parameters as a function of the composition were investigated by the x-ray diffraction method. The solid solutions with a perovskite structure were formed as a single phase with x up to 0.9. For the composition of x = 1.0, metastable La-Ti-O perovskite phase with a small amount of the impurity phase, La2Ti2O7, was obtained. Simulation of x-ray diffraction patterns based on the defect structure model shows that the structure of the La-Ti-O perovskite phase includes randomly distributed cation vacancies at the A-site, namely (La2/3□1/3)TiO3.

The upconversion of infrared radiation into visible light has been studied in heavy metal oxyfluoride glass-ceramics co-doped with Yb3+ and Tm3+ ions at 300 K. The general composition of the compounds is 69.9PbF2 + 7.5WO3 + 7.5MO2 + 15YbF3 + 0.1TmF3 (M = Si, Ge, Zr, Te, and Th). Two main upconversion emissions were observed. They are centered at 477 and 775 nm, corresponding to the 1G4 → 3H6 and 3F4 → 3H6 transitions, respectively. Slopes of the emission intensity versus excitation power measurements indicate that the blue emission is due to three-photon absorption, while two-photon absorption processes are responsible for the red emission. A comparative method was used to measure the upconversion efficiencies under 16.5 mW/cm2 excitation power. Measurements were made after the compounds were annealed at 450 °C for 4 h. The best conversion efficiencies were obtained for the compound having silicon (Si). They are 28 × 10−6 for the blue and 18 × 10−2 for the red emission.

Brominated, anodically oxidized, and pristine p-100 carbon fiber reinforced tin-lead alloy composites were fabricated by squeeze casting. The fibers were brominated by bromine vapor for 48 h and then desorbed at 200 °C in air for 12 h. The anodic oxidation treatment of fibers involved electrochemical etching in a dilute sodium hydroxide electrolyte for 3 min, or immersing in nitric acid for 72 h. The composites containing surface-treated carbon fibers had higher tensile and interlaminar shear strength than the ones containing pristine carbon fibers. The composite containing brominated carbon fibers had better tensile strength than the other two surface treatments.

Diamond nucleation on unscratched silicon substrates coated with thin films of hard carbon was investigated experimentally with a microwave plasma-assisted chemical vapor deposition system. A new pretreatment process was used to enhance the nucleation of diamond. Relatively high diamond nucleation densities of ∼108 cm−2 were achieved by pretreating the carbon-coated silicon substrates with a methane-rich hydrogen plasma at a relatively low temperature for an hour. Scanning electron microscopy and laser Raman spectroscopy studies revealed that diamond nucleation occurred from nanometer-sized spherical particles of amorphous carbon produced during the pretreatment. The nanoparticles possessed a structure different from that of the original hard carbon film, with a broad non-diamond Raman peak centered at ∼1500 cm−1, and a high etching resistance in pure hydrogen plasma. The high diamond nucleation density is attributed to the significant percentage of tetrahedrally bonded (sp3) atomic carbon configurations in the nanoparticles and the presence of sufficient high-surface free-energy sites on the pretreated surfaces.

Microwave plasma-enhanced chemical vapor deposition of diamond films on silicon carbide and tungsten carbide (with 6% cobalt) surfaces using fluorocarbon gases has been demonstrated. No diamond powder pretreatment is necessary to grow these films with a (100) faceted surface morphology. The diamond films are characterized by scanning electron microscopy and Raman spectroscopy. The proposed nucleation and growth mechanism involves etching of the noncarbon component of the carbide by atomic fluorine to expose surface carbon atoms and diamond nucleation and growth on these exposed carbon atoms. Hydrogen is necessary in the growth process to limit the rapid etching of the carbide substrates by corrosive fluorine atoms.

The early stages of microwave-plasma assisted CVD of diamond on fused silica and silicon substrates were investigated. Nucleation densities on fused silica were somewhat lower than on silicon; however, the diamond growth rates on fused silica were faster. These results suggest that the substrate alters the plasma chemistry near the substrate. Transmission electron microscopy showed a relatively smooth interface between the diamond grains and the SiO2 surface. At low nucleation densities, the growth kinetics on both substrates were linear (i.e., the average feature size was proportional to the deposition time), which indicates that the growth kinetics were initially controlled by reaction(s) at the growing diamond surfaces. The transition to nonlinear growth kinetics observed at higher nucleation densities was probably caused by mass-transport limits.

There is currently considerable interest in producing high temperature capability graphitic materials by first weaving graphite fiber tows (yarns) into a “preform” structure, followed by densification via cracking of precursor compounds such as dimethyldichlorosilane within the pores (macro and micro) at high temperature. The model described in this paper addresses this densification process, treating diffusion of gaseous species both within the macropores (spaces between the tows) and the micropores (spaces between individual fibers in the tows) and finite kinetics associated with the cracking of the precursor gas (treated parametrically). The resulting model is used to examine the effects of temperature distributions through cylindrical preforms on ultimate densification distribution. As might be expected (and as observed experimentally), uniform temperature through the preform leads to premature full densification of the pore structure at the periphery of the cylinder (blocking further densification in the interior), leading to severe porosity in the interior regions. Effects of externally imposed nonuniform temperature profiles (possibly via microwave heating) in alleviating this problem are examined, and it is shown that proper profiling can lead to nearly complete uniform densification throughout the preform.

We present a computer simulation study of thin crystalline multilayers constructed from two fcc solids with differing lattice constants and binding energies. Initially the two solids have the same orientation, and the interface is perpendicular to the common [100] direction. We then minimize the energy of the system at zero temperature or equilibrate it at a finite temperature. Both materials are described by Lennard-Jones interatomic potentials. A novel technique for analyzing local atomic ordering, common neighbor analysis, is used to identify structural characteristics in these systems. As we gradually vary the lattice mismatch between the two solids, several structural changes are observed in the layers of smaller atoms after energy minimization. At a mismatch larger than 14%, the layers transform into the hep structure, while at smaller mismatches extended structural defects are generated. At elevated temperatures, the hcp structure is transformed back to fcc, and the structure defects disappear.

“Morphology of TiSi2 and ZrSi2 on Si(100) and (111) surfaces” [J. Mater. Res. 9, 1214–1227 (1994)]