Thermal aging and irradiation experiments were carried out in Fe–Ni–Cr base alloys containing Ti or Nb as well as low levels of oxygen, nitrogen, and carbon. After aging, fine dispersions of TiC and NbC were formed. However, after irradiation the Ti-containing alloy precipitated Ti(N,O) rather than TiC, while the Nb-containing alloy precipitated NbC. Analysis of the energetics of these reactions reveals that the Ti(N,O) phase is thermodynamically more stable than the TiC phase, while the NbC phase is more stable than the NbO phase. These results are therefore consistent with observed behavior. While it is well known that irradiation can drive a system away from equilibrium, the present results show that irradiation also can catalyze the formation of a more stable phase at the expense of a persistent metastable phase.

Single-crystal x-ray diffraction measurements made on a millimeter-size single icosahedral quasicrystal of an Al–Li–Cu alloy are reported. The point symmetries observed directly by real-time transmission Laue x-ray diffraction and the measured angles between the major symmetry axis are consistent with an icosahedral quasicrystal, and the peaks observed in the single-crystal diffraction scans are found to be indexable with six indices that belong to a primitive icosahedral Bravais quasilattice.

It is shown that both icosahedral Al–Mn–Si and Mg–Al–Zn alloys give rise to the same variety of electron diffraction patterns as documented for icosahedral Al–Mn alloys. Subtle variations in intensity are ascribed to a different decorational motif in terms of the Mackay icosahedron and the Pauling triacontahedron. Icosahedral Al–Mn–Si alloys do not appear to be ordered on a superlattice basis.

An x-ray diffraction technique has been developed to make in-situ measurements of hydrogen concentration profiles from which diffusivity and solubility values are calculated. Hydrogen is supplied to the metal surface by cathodically polarizing it in a bath of 1N H2SO4 electrolyte. The incident x-ray beam penetrates a thin layer of electrolyte solution at the surface of the sample, thus, x-ray diffraction profile changes can be recorded as a function of charging time and temperature. The applied potential prevents outgassing of the specimen during the measurement. The x-ray diffraction profiles are deconvoluted to remove the α1/α2 doublet and noncompositional broadening effects. Composition-depth profiles are then obtained from an intensity band transformation of the deconvoluted data. A diffusion coefficient is determined by fitting a solution to Fick's second law to the concentration-depth profile. The technique described here was used to measure hydrogen diffusivity in stainless steel in the temperature range 20°–80°C.

Ion-beam mixing in the Bi/Sb system using Ne+, Ar+, and Kr+ ions in the energy range 40–110 keV has been investigated by Rutherford backscattering analysis. The mixing is shown to be temperature independent in the region of 40–250 K; at higher temperatures the mixing per ion increases rapidly with temperature. Initially, a square-root dependence of the mixing on the ion dose was observed. At higher doses a saturation effect is obtained as the Sb becomes uniformly distributed in depth throughout the film. Also, the mixing was found to increase linearly with the energy deposited into atomic displacement collisions at the Bi/Sb interface. Alloys of Bi1−x Sbx (0<x<0.5) have been produced. The thermoelectric power of the fully mixed alloys reaches a maximum value at an alloy composition of Bi0.87 Sb0.13. The thermoelectric power for partially mixed alloys exhibits almost the same dependence on Ar+ dose as the amount of mixing.

The mercury cation Hg2+ is used to intercalate NbF−6 and TaF−6 anions into pyrolytic graphite (HOPG). The Hg2+ cation in Hg (NbF6)2 and Hg(TaF6)2 oxidizes HOPG to form stage-3 compounds. The Hg2+2 cation is also used as an oxidant to intercalate AsF−6 and SbF−6 ions into graphite. The reduced products of the reactions are identified by Raman spectra. The intercalation compounds are characterized by (00l) x-ray diffraction, and the intercalants are identified with mass spectrometer analysis.

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.

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.

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.

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.

Molecular dynamic calculations have been made on glasses in the ZnCl2–KBr system in order to estimate the infrared (IR) absorption of these glasses. Oxygen-free glass was estimated to be transparent up to 25 μm. Glasses containing oxygen impurities were estimated to be transparent only up to 16 μm, with a weak absorption band around 10.4 μm. This agrees with experimental results of glasses in the ZnCl2–KBr–PbBr2 system.

The influence of In and Ag atoms on the dc electrical conductivity and optical properties in the short wavelength edge region in Ge20Sb10S70 and Ge30Sb10S60 glasses has been examined. Contrary to the effect of In atoms, the Ag atoms at concentration levels below 4 at. % of Ag significantly influence the dc conductivity. Changes of the optical properties are less significant, and they are affected in a similar way by incorporation of In and Ag atoms into a glassy matrix. It is supposed that some of the Ag atoms are positively ionized to an Ag+ species that remains in the network. The 5s1 electron of Ag interacts with D+ states making, in the final state, an increase of D− defect states. Thus the Fermi level is shifted to the valence band and the dc conductivity increases.

The variation of resistivity of the lithium fast-ion conductor Li3+y Ge1−yO4 (y = 0.25, 0.6, 0.72) has been studied with hydrostatic pressure up to 70 kbar and compared with that of Li16−2x Znx (GeO4)4(x = 1, 2). Both types showed pronounced resistivity maxima between 20–30 kbar and marked decrease thereafter. Measurements as a function of temperature between 120–300 K permitted the determination of activation energies and prefactors that also showed corresponding maxima. The activation volumes (ΔV) of the first type of compound varied between 4.34 to −4.90 cm3/mol at 300 K and decreased monotonically with increasing temperature. For the second type ΔV was much smaller, varied with pressure between 0.58 and −0.24 cm3/mol, and went through a maximum with increasing temperature. High-pressure studies were also conducted on aged samples, and the results are discussed in conjunction with results of impedance measurements and nuclear magnetic resonance (NMR) studies. The principal effect of pressure appears to be variations of the sum of interatomic potentials and hence barrier height, which also causes significant changes in entropy.

For liquid phase epitaxial (LPE) growth of BiYIG films, MoO3 is shown to be a flux modifier that increases Bi content xBi, and growth-induced anisotropy Ku8, for MoO3 flux concentrations up to 12 mol %. The addition of MoO3 to PbO–Bi2O3 fluxed garnet melts caused the saturation temperature to increase at a rate of 7 deg/mol % while growth rates decreased. For a given amount of supercooling, ΔTs, xBi increased with MoO3 flux content up to 12 mol %. A linear dependence of xBi on ΔTs, was observed for all MoO3 concentration levels. The anisotropy increased both with supercooling and with MoO3 flux concentration. The Kgu can be represented by a two-variable model, Kgu = A +BxBi + C4IIMs, where B increases from 143–213 kerg/cm3 per Bi atom per formula unit as the MoO3 content of the flux increases from 0–12 mol %. The density of the melt decreases with increased MoO3 content. A melt based on a 15 mol % MoO3 flux is less dense than gadolinium gallium garnet.

Log wavelength optical photons in a quanternary In1−x Gax AsyP1−y alloy are investigated based on the Green's function technique utilizing the concentration-dependent modified rigid ion model (MRIM). In order to obtain four-mode behavior in an A1−xBxCyD1−y quaternary alloy, formation of two cells AB and CD has been considered. In addition to the interactions betwen A, B, C, and D in their concentration ratios with a nonrandom ness parameter, the intercell and the intracell interactions are also taken into account. The results for the In1−xGaxAsyP1−y quaternary alloy are found to be in satisfactory agreement with the available experimental results.

A compilation is made of the crystallographic mechanisms whereby (simulated) radwaste species are incorporated in the “synroc” phases zirconolite, perovskite, hibonite, and “hollandite.” From these data and consideration of the crystal chemical criteria of valence and effective ionic radii, the most probable host phases for transuranic isotopes are identified. The distinction is drawn between incorporation of radwaste species as dilute homogeneous, continuous solid solutions and as heterogeneous, noncontinuous solid solutions. It is shown that compositional variations at the nanometer level are frequently accompanied by the generation of new interstices within extended defects, which are suitable for the location of radwaste. Nuclides that are unstable towards beta and gamma decay lead to transmutation-induced changes in stoichiometry. Crystallochemical mechanisms that minimize structural disruption during the formation of radiogenic species are discussed. Thermally promoted recovery of metamict phases, which were rendered aperiodic by direct atomic displacements of alpha-recoil nuclei, are examined in terms of recrystallization via the hierarchial arrangement of space groups. An evaluation is made of the hydrothermal durability of synroc phases under conditions likely to be experienced by the wasteform should the repository be breached by groundwaters shortly after disposal.