The embedded atom method [M. S. Daw and M. I. Baskes, Phys. Rev. B 29, 6443 (1984) used to calculate phase stability, lattice vibrational frequencies, point defect properties, antiphase boundary energies, and surface energies and relaxations for Ni3Al. The empirical embedding functions and core-core repulsions used by this method are obtained. The equilibrium phases for the Ni-rich half of the composition range of Ni–Al are determined for 1000 K and compared with experiment. The elastic constants and vibrational modes of Ni3Al are calculated and the elastic constants are compared with experiment. The formation energy, formation volume, and migration energies of vacancies are computed, and it is found that the formation energy of vacancies on the Ni sublattice is less than that on the Al sublattice. The (100) antiphase boundary is shown to be significantly lower in energy than the (111) antiphase boundary. The surface energies and atomic relaxations of the low index faces are computed, and it is shown that for the (100) and (110) faces that the preferred surface geometry corresponds to the bulk lattice with the mixed composition plane exposed.

The crystal structure and chemical composition of the intermetallic phase in a Fe-20%Cr-4%Al-0.5%Y (wt. %) alloy were investigated by electron microscopy. Convergent beam diffraction studies revealed that the intermetallic phase forms in three different crystal structures that could coexist in a single grain of the phase. The dominant crystal structure was shown to be hexagonal (a = 0.85, c = 0.84 nm) with a space group most likely to be P63/mmc. Within the hexagonal phase, regions of a rhombohedral crystal structure (a = 0.85, c = 1.26 nm) were observed that had grown in without an apparent phase boundary separating the two crystal structures. The third crystal structure was determined to be monoclinic (a = 0.97, b = 0.85, c = 1.07 nm, and beta = 97.3°) and formed by twinning on the {10$\overline 1$1} planes of the hexagonal phase. The chemical compositions of regions with different crystal structures were comparable and the stoichiometry of the intermetallic phase corresponds to (Fe,Cr)17 (Al,Y)2. The relationship of the observed crystal structures to those previously reported is discussed.

The thin-film interactions of Au with Ti, Zr, V, and Nb have been investigated between 350C and 700°C with Rutherford backscattering spectroscopy (RBS) and x-ray diffraction (XRD). Initially the most Au-rich phase is formed, except. with V, and it is followed sequentially by the more metal-rich ones in an increasingly layer-by-layer fashion. For Au reactions on Ti and Nb, all the intermetallic phases on the phase diagrams were observed. In the formation of Au4Ti, Au is the dominant moving species.

Deposited thin films of Cr and Ni on Cu substrates have been melted and intermixed with a frequency-doubled Q-switched Nd:YAG laser. The laser pulses melt the thin films and a shallow portion of the substrate. Resolidification interface volocities are on the order of 1–10 m s−1. Rutherford backscattering, Auger spectroscopy, and energy dispersive x-ray mapping have been used to characterize the elemental distribution. Channeling and transmission electron microscopy were used to investigate the microstructure of the surfaces produced. In contrast to the binary Cr–Cu system, where extended solid solutions are produced, the Cr–Ni–Cu system results in a metallic glass surface. We have found that these metallic glass surfaces, which have been dubbed “stainless coppers,” exhibit excellent hydrogen sulfide corrosion resistance. Their contact resistance is low and stable over long periods of time and through tens of thousands of electronic dial switching cycles.

The effects of pulsed laser radiation on the corrosion resistance, surface morphology, and composition of liquid-quenched amorphous Fe32Ni36Cr14P12B6 (Allied Corporation Metglas¯ 2826A) are reported. Scanning electron microscopy, Auger depth profiling, and x-ray diffraction were used to characterize the surface, while the corrosion resistance was determined by anodic polarization in H2SO4. The surface of the as-received melt-spun ribbons exhibited many defects, including cracks, compositional irregularities, and microcrystals of Ni5P4. These microcrystals differ from those found upon bulk crystallization. Melting and rapid solidification by radiation with a Q-switched Nd–YAG laser [30 ns full width at half maximum (FWHM)] modified the surface morphology (leaving composition constant), removing the microcrystals and cracks and reducing the carbon and oxygen contamination. The reduction of these surface defects resulted in improved corrosion resistance of the Metglas¯ 2826A ribbon. For example, spontaneous passivation is observed for the laser-treated samples, as opposed to critical current densities of 10μA/cm2 and 1000μA/cm2 for the as-received amorphous and crystallized Metglas¯ alloy, respectively.

Relaxation effects in Fe–B metallic glasses have been studied through measurements of the Curie temperature (Tc) and changes of enthalpy. A monotonic increase in Tc with annealing temperature is observed for all compositions due to irreversible structural relaxation. This increase continues until the start of surface/bulk crystallization. The observed decrease in Tc, upon further annealing is attributed to the strain introduced in the partially glassy system, which masks any evidence for reversible structural relaxation. Enthalpy measurements do show a small reversible structural relaxation. The magnitude of the effect is about a factor of 6 smaller than in ternary metalloid-containing glasses.

Inert particles that do not contribute to the densification of a composite powder compact are visualized as located on network sites; the network is defined by the distribution of the particles in the powder matrix. Because the distances between neighboring network sites are not identical, the strain produced by the sintering powder between all inert particle pairs cannot be the same as that for the powder compact without the inert particles. The constrained network model is based on the hypothesis that the densification of the composite will be constrained by the network and will mimic that of the network. The shrinkage of the network, and thus the densification of the composite, is estimated with a periodic network. A distance between the minimum and maximum site pairs within the unit cell defines the distance between site pairs in the random network where the powder between the particles densifies in the same manner as that for the powder without the inert particle. When the particles form a continuous touching network, composite shrinkage and densification is nil. The chosen lattice must also conform to this condition. A simple relation was developed relating the densification behavior of the composite to that of the matrix without the inert particles and the parameter associated with the chosen lattice. By choosing the lattice formed by the tetrakaidecahedron unit cell (volume fraction of particles for a touching network = 0.277), remarkable agreement was achieved for the experimental data concerning the densification behavior of the ZnO/SiC composite system reported by De Jonghe et al. [L. C. De Jonghe, M. N. Rahaman, and C. H. Hsueh, Acta Metall. 34, 1467 (1986)]. The universal nature of this lattice for other composites is discussed with respect to site percolation theory. The application of this concept to powder compacts containing either whiskers or agglomerates is briefly discussed.

An investigation was made of the effect of Y2O3 in solid solution in ZrO2 on the phases that are formed when ZrO2 is reacted with either N2 or Si3N4. The results suggest that the Zr–oxynitride phase can be predcluded as a reaction product when the Y2O3 content of the ZrO2 is ≥4 mol %. Dense Si3N4/ZrO2(+ Y2O3) composites were fabricated, which did not degrade during oxidation at temperatures %le; 1000°C. Severe degradation was observed for composites containing the Zr-oxynitride phase. The fracture toughness of the Si3N4/ZrO2(+ Y2O3) composites increased with ZrO2 content.

The OH− and OD− vibrational frequencies in stoichiometric and nonstoichiometric MgAl2O4 were measured. The nonstoichiometric material had a Al/Mg ratio of 7. The diffusion coefficient of deuterons in the nonstoichiometric material at 1600 K is about 6 ± 3 ⊠ 10−8 cm2/s. Deuterons can readily be swept out by applying an electric field at temperatures above 1000 K.

Cesium molybdenum bronze, CsMo4xO12, is a recently discovered highly anisotropic semiconductor that crystallizes in the monoclinic system with space group C2/m and four formulas in the unit cell. The lattice constants at 295 K are a = 19.063(5), b = 5.5827(23), c = 12.1147(23) Å, and β = 118.94(2)°. The integrated intensities of 13.529 reflections within a full sphere of reciprocal space with radius (sin θ)/λ≤0.75 Å−1 were measured on a CAD-4 diffractometer with MoKα radiation, resulting in 12 553 reflections above background. Correction and averaging in C2/m gave 1923 significant and independent structure factors, for an internal unweighted agreement factor of 0.0288. The crystal structure was solved from the Patterson function and Fourier series and refined by the method of least squares. The Cs atoms occupy two different sites; both, as well as the nine independent O atom sites, are fully occupied, but the four independent Mo atom sites contain significant Schottky defects, with x = 0.132(8) in the chemical formula. All metal atoms undergo significant anharmonic motion. The final agreement factor R = 0.0269, Two Mo atoms are tetrahedrally, the other two octahedrally, coordinated. The average tetrahedral Mo–O distance is 1.761 Å, the octahedral distance is 1.950 Å. Bond length–bond strength considerations suggest that Mo6+ ions (almost) completely occupy the tetrahedral sites whereas the octahedral sites are (almost) half occupied by Mo6+, half by Mo5+ ions, resulting in charge balance. Infinite polyhedral sheets of corner-sharing Mo–O octahedra and tetrahedra form normal to the a axis, separated by linear arrays of Cs+ ions. The resistivity in this and other low-dimensional alkali molybdenum bronzes is a minimum (10−1–10−2 Ω cm) in the direction along which both corner-sharing octahedra, and the shortest contacts between cations arranged in infinite chains, form. The resistivity normal to the polyhedral sheets is about 2 orders of magnitude greater, at ∼ 10 Ω cm.

An upper limit is placed on the overheating at the liquid/solid interface during melting of (100) Si at high interface velocity. The limit is based on an energy-balance analysis of melt depths measured in real time during pulsed-laser melting of Si on sapphire. When combined with previous measurements of the freezing kinetics of Si, this limit indicates that the kinetics of melting and freezing are nonlinear, i.e., the undercooling required to freeze at modest (15 m/s) velocities is proportionately much greater than the overheating required to melt at high (190 m/s) velocities.

Experiments are described in which hydrogen is injected into silicon by various techniques and detected by the neutralization of boron acceptor sites. Wet chemical etching is shown to inject protons several microns in a few seconds; this experiment is used to set a lower limit on the diffusivity of hydrogen of ⋍2⊠10−11 cm2/s at 300 K, a number in reasonable agreement with prior estimates deduced by Van Wieririgen and Warmholtz from high-temperature permeation measurements. A number of experiments are reported to elucidate the mechanism for “unintentional” hydrogenation occurring during argon ion bombardment. The data suggest that this effect is caused by bombardment-induced injection of hydrogen from surface H2O/hydrocarbon contaminants.

The annealing behavior of ion-implanted α-SiC single crystal was determined for samples implanted with 62 keV 14N to doses of 5.5X1014/cm2 and 8.0X1016/cm2 and with 260 keV 52Cr to doses of 1.5X1014/cm2 and 1.0X1016/cm2. The high-dose samples formed amorphous surface layers to depths of 0.17 μm (N) and 0.28 μm (Cr), while for the low doses only highly damaged but not randomized regions were formed. The samples were isochronically annealed up to 1600°C, holding each temperature for 10 min. The remaining damage was analyzed by Rutherford backscattering of 2 MeV He+, Raman scattering, and electron channeling. About 15% of the width of the amorphous layers regrew cpitaxially from the underlying undamaged material up to 1500°C, above which the damage annealed rapidly in a narrow temperature interval. The damage in the crystalline samples annealed linearly with temperature and was unmeasurable above 1000°C.

Results from x-ray photoelectron spectroscopy (XPS or ESCA), low-energy ion scattering spectrometry (LEIS or ISS); and Fourier transform infrared spectroscopy (FTIR) analyses are presented for unmodified and modified poly (methylmethacrylate) (PMMA) polymer films. Analysis of the unmodified PMMA polymers (isotactic, syndiotactic, and atactic) via ESCA, ISS, and FTIR, established the surface composition, bonding, and functionality before the modification was employed. An rf-plasma glow discharge created from an Ar/H2O gas mixture at different exposure times and power levels was used to treat the polymer surface. Subsequent ESCA, ISS, and FTIR analyses of these modified PMMA's show the effects of surface modification in terms of a model of structural differences, over a limited depth (50–100 Å). The composition and functionality changes of the resulting surfaces are discussed with respect to proposed mechanisms of the plasma reaction and differences in tacticity of the reactant. A two-step reaction mechanism involving reactive decarboxylation/reduction followed by H2O adsorption is proposed to understand the spectroscopic results.

Results from the x-ray photoelectron spectroscopy (XPS or ESCA), ion scattering spectroscopy (ISS or LEIS), and Fourier transform infrared spectrometry (FTIR) analyses are presented for unmodified and modified poly (methylmethacrylate)/poly (methacrylic acid) (PMMA/PMAA) copolymer films. Analyses of the unmodified PMMA/PMAA copolymer series, via ESCA, ISS, and FTIR, established the surface composition and functionality of the PMMA/PMAA copolymers before the H2O/Ar rf-plasma treatment was employed. The ESCA, ISS, and FTIR analysis of these modified PMMA/PMAA copolymers show that surface modification over a limited depth (50–200 Å) has occurred. The composition, bonding, and functionality changes of the surfaces are discussed. A two-step modification mechanism (surface reduction of the PMMA/PMAA copolymer followed by H2O adsorption) is proposed to interpret the spectroscopic results.