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.

Field emitter array cathodes were fabricated from unidirectionally solidified composites of tungsten fibers in an insulating yttria-stabilized-zirconia (YSZ) matrix. A close-spaced molybdenum gate film (extractor) was formed utilizing c-beam evaporation of alumina as an insulator, which was overlayed by the molybdenum extractor. The high resistivity of the composite matrix coupled with the alumina insulator resulted in low leakage current and permitted dc operation of the device. Emission testing demonstrated current densities of 1–5 A/cm2 with leakage in the μA range for applied potentials of 125–200 V. Variation of emitter tip geometries from hemispheres to right circular cylinders to pointed cones produced increases in emission consistent with reduced tip radii.

The growth of an oriented anatase grain structure from the post-deposition annealing of amorphous reactive ion-beam-deposited thin films of titanium oxide has been demonstrated. The transformation has been observed directly by electron microscopy and the crystallization of the films occurs only when their thicknesses are greater than about 50 nm. Substrate effects were not found to be significant to the crystallization, which could also be induced by annealing freestanding films. The transformation processes can be described in terms of existing theories of crystal growth where the amorphous film is described as a supercooled liquid.

Analytical expressions describing the various thermodynamic phases in binary systems can be derived by the CALPHAD approach, whereby the parameters in these expressions are obtained from fits to measured phase equilibrium data. Extrapolations of these models can be used to predict metastable equilibria. Different thermodynamic models proposed for the Ni–Ti and the Cu–Ti systems are used to calculate the T0 curves that are relevant to the prediction of the glass-forming range in rapidly cooled molten alloys. Although all the models give acceptable fits for the equilibrium range for which they were derived, significant differences are found for the metastable regime. The problems that need to be addressed in order to improve the extrapolations into the metastable regime are discussed. Simple thermodynamic considerations predict that the glass-forming range for rapidly quenched alloys exceeds that for amorphous alloys synthesized by isothermal solid-state interdiffusion reactions.

High-temperature crystal structures of NZP (Na1+xZr2P3−xSixO12) have been determined by x-ray measurements made on single crystals. Thermal expansion of NZP (x = 0.11) parallel to the hexagonal c axis is positive (about 22.4 ⊠ 10−6°C−1 between 25° and 700°C), whereas expansion perpendicular to c is slightly negative (about 5.4 ⊠ 10−6°C−1), resulting in an average volume thermal expansion of 11.8 ⊠ 10−6°C−1. A proposed structural model to interpret this anisotropic thermal expansion of NZP is tested to prove the model's validity. In this model the rotation of the phosphate tetrahedron is coupled to the rotation of the zirconium octahedron. The observed thermal expansions of sodium, zirconium, and phosphorus cation coordination polyhedra are 10.8, 0.00, and −0.23 (all × 10−6°C−1), respectively. The large thermal expansion of the sodium site is offset by rotations in the Zr–P polyhedral framework, thus yielding the low net expansion of NZP.

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 electrical conductivity has been measured for the glasses in the system B2O3–Li2O–Li2X2(X = F, Cl, Br), where Li2O is replaced by Li2X2 with Li content kept constant. The conductivity decreases for F glasses and increases for Cl and Br glasses with increasing halide ion content, which is caused by the increase in the activation energy for F glasses and the decrease for Cl and Br glasses. The analysis of the activation energy in terms of the Anderson-Stuart model indicates that, with the increase in LiX, Δ Eb, (the electrostatic energy) increases for F glass, whereas ΔEs (the strain energy) and ΔEb decrease for Cl or Br glasses. The effects of F− and other halide ions are attributed to a stronger interaction between Li and F, and to expanded and weakened glass network due to accommodation of Br− and Cl− ions.

Studies show that Ba2M Cu3O6.5 + x can be treated like a pseudobinary oxide MeOx with metal framework Me = Ba2YCu3O6.5. An approximate phase diagram was derived by thermogravimetry, differential thermal analysis, strain gauge measurements, and annealing at varied oxygen partial pressure.

Electron paramagnetic resonance (EPR) has been measured on powdered YBa2Cu3O7−δ at 9 GHz and at variable temperature 4.2 K ≤ T ≤ 293 K. The decrease of the mean Landé factor value ḡ from 2.22 to 2.07, between T = 4 K and T = Tc, is ascribed to a hole being transferred from copper to oxygen.

Nickel orthosilicate (Ni2SiO4) has been found to decompose into its component binary oxides in oxygen potential gradients at 1373 K. Nickel oxide was formed at the high oxygen potential boundary, while silica was detected at the low oxygen potential side. Significant porosity and fissures were observed near the Ni2SiO4/SiO2 interface and the SiO2 layer. The critical oxygen partial pressure ratio required for decomposition varied from 1.63 to 2.15 as the oxygen pressures were altered from 1.01 ⊠ 105 to 2.7X 10−4 Pa, well above the dissociation pressure of Ni2SiO4. Platinum markers placed at the boundaries of the Ni2SiO4 sample indicated growth of NiO at the higher oxygen potential boundary, without any apparent transport of material to the low oxygen potential side. However, significant movement of the bulk Ni2SiO4 crystal with respect to the marker was not observed. The decomposition of the silicate occurs due to the unequal rates of transport of Ni and Si. The critical oxygen partial pressure ratio required for decomposition is related both to the thermodynamic stability of Ni2SiO4 with respect to component oxides and the ratio of diffusivities of nickel and silicon. Kinetic decomposition of multicomponent oxides, first discovered by Schmalzried, Laqua, and co-workers [H. Schmalzried, W. Laqua, and P. L. Lin, Z. Natur Forsch. Teil A 34, 192 (1979); H. Schmalzried and W. Laqua, Oxid. Met. 15, 339 (1981); W. Laqua and H. Schmalzried, Chemical Metallurgy—A Tribute to Carl Wagner (Metallurgical Society of the AIME, New York, 1981), p. 29] has important consequences for their use at high temperatures and in geochemistry.

The low-temperature (120°–245°C) structural relaxation of Metglas¯ 2826B (Ni49Fe29P14B6Si2) amorphous alloy was investigated for samples subjected to a tensile stress in the range of 20–400 MPa during annealing. The stress-annealed samples demonstrated a much smaller increase of microhardness than was observed in similarly annealed ribbons without a stress. Further heat treatment of the stress-annealed specimens, this time without the stress, was capable of increasing the microhardnesses of only some ribbons to values equal to those of samples similarly heat treated initially without a stress. An additional exothermic peak in the differential scanning calorimetry (DSC) thermograms of the stress-annealed specimens indicated the presence of a more disordered structure at room temperature, which was found to correlate with the lower microhardness values. Otherwise, those artifacts of the DSC thermograms that were characteristic of samples annealed without a stress were still present in the stress-annealed ribbons. No effect on the crystallization temperature was noted but the glass transition temperature was increased in the stress-annealed case with respect to values attained when the stress was absent during heat treatment. A reduction in the degree of embrittlement of those samples annealed with a tensile stress was a further indication of more disorder in the stress-annealed ribbons.

Ion-beam mixing of Ti layers with sintered α-SiC and hot-pressed Si3N4 was measured for 1 McV Au+ at doses of 1X1016 cm−2 and 5X1016 cm−2. Rutherford backscattering (RBS) and cross-section transmission electron microscopy (XTEM) were used to evaluate the mixing. Mixing was observed in Ti/SiC system; however, there was no mixing in Ti/Si3N4 system. Results are discussed in light of the enthalpy of mixing criterion for metal-insulator systems.

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.

The electron-induced decomposition (EID) of SiO2 overlayers on various high surface area oxide substrates was studied using Auger electron analysis (AES). Bulk SiO2 was stable upon electron bombardment, but bulk Al2O3 decomposed readily to elemental Al when the primary electron beam energy was 2 keV and the beam current was 6–16 μA. On the other hand, SiO2 overlayers having an average thickness of about 10 Å on Al2O3 decomposed selectively under the same conditions. In contrast to Al2O3 substrates, SiO2 overlayers on TiO2, ZrO2, and MgO were quite stable to the same electron bombardment. Therefore it is concluded that Al2O3 accelerates the EID of SiO2 overlayers and the SiO2 overlayer suppresses EID of Al2O3 substrates.

An indentation-strength formulation is presented for nontransforming ceramic materials that show an increasing toughness with crack length (T curve, or R curve) due to the restraining action of interfacial bridges behind the crack tip. By assuming a stress-separation function for the bridges a microstructure-associated stress intensity factor is determined for the penny-like indentation cracks. This stress intensity factor opposes that associated with the applied loading, thereby contributing to an apparent toughening of the material, i.e., the measured toughness in excess of that associated with the intrinsic cohesion of the grain boundaries (intergranular fracture). The incorporation of this additional factor into conventional indentation fracture mechanics allows the strengths of specimens with Vickers flaws to be calculated as a function of indentation load. The resulting formulation is used to analyze earlier indentation-strength data on a range of alumina, glass-ceramic, and barium titanate materials. Numerical deconvolution of these data determines the appropriate T curves. A feature of the analysis is that materials with pronounced T curves have the qualities of flaw tolerance and enhanced crack stability. It is suggested that the indentation-strength methodology, in combination with the bridging model, can be a powerful tool for the development and characterization of structural ceramics, particularly with regard to grain boundary structure.

A method using synchrotron radiation parallel beam x-ray optics with a small incidence angle α on the specimen and 2Θ-detector scanning is described for depth profiling analysis of thin films. The instrumentation is the same as used for Θ:2Θ synchrotron parallel beam powder diffractometry, except that the specimen is uncoupled from the detector. There is no profile distortion. Below the critical angle for total reflection αc, the top tens of Angstroms are sampled. Depth profiling is controlled to a few Angstroms using a small α and 0.005° steps. The penetration depth increases to several hundred Angstroms as α approaches αc. Above αc there is a rapid increase in penetration depth to a thousand Angstroms or more and the profiling cannot be sensitively controlled. At grazing incidence the peaks are shifted several tenths of a degree by the x-ray refraction and an experimental procedure for calculating the shifts is described. The method is illustrated with an analysis of iron oxide films.

High-resolution transmission electron microscopy (HRTEM) and ellipsometry techniques have been employed to measure thicknesses of silicon oxide, grown at 800°C in dry oxygen, in the thickness range of 2–20 nm. While the oxide growth data measured from TEM obey a nearly linear behavior, those obtained from ellipsometry are seen to vary nonlinearly. The interface structure as function of the increasing oxide thickness was studied using HRTEM. At these oxidation temperatures, the earlier reported variations of roughness at the interface on the oxide thickness for oxides grown at 900°C are not seen. Attempts aimed at correlating the high-resolution transmission electron micrographs with some physical parameters like the refractive index and the dielectric breakdown lead to considerations of the importance of the effect of protrusions of silicon atoms of 1 mm size into SiO2 layers on the interface properties. These findings lead to explanations of some key features concerning the refractive index and density of thin SiO2.

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.

The x-ray photoemission spectroscopie (XPS) data from different pelletized samples of the 90 K superconductor Ba2YCu3O7−δ (where δ∼0.2) have been obtained. The valence band spectrum (recorded at 300 and 170 K), which is composed of contributions from both the Cu 3d and O 2p levels, is compared with the full potential linearized augmented plane wave (FLAPW) calculated electronic density-of-states (DOS) reported by Massidda et al. and Mattheiss and Hamann. The experimental data indicate a relatively low DOS at the Fermi level. Detailed measurements of the core level Cu 2p, O 1s, Ba 3d, 4d, and Y 3d spectra of the superconducting and related standard materials, are presented. Data for the superconducting material were recorded in the freshly prepared form as well as after scraping in situ. The Cu 2p core level, satellite, and Auger spectra for the various samples were carefully examined in order to assess the possibility of the presence of Cu3+ ions in Ba2YCu3O7-δ. It is observed that surface reaction in air to form carbonates and hydroxides occurs readily in the superconducting material.

Synthetic gray-blue diamonds were used as anvils in a diamond anvil cell to produce a pressure of 125 GPa (1.25 Mbar) in a gasketed sample. Pressure was measured by x-ray diffraction methods by using gold and iron as a calibrant and also by optical methods based on the shift of the fluorescence peaks of ruby with pressure. The future potential of synthetic diamonds for ultrapressure research is discussed.