We present results of atom superposition and electron delocalization molecular orbital (ASED-MO) calculations of interactions of interstitial H with substitutional B and N in diamond. Nearest-neighbor and next-nearest-neighbor C atoms were relaxed in geometry depending on the cluster size, XC34H36 or XC70H60, respectively, where X = B or N and the H atoms saturate the surface dangling radical orbitals of the models. A small Jahn-Teller distortion occurs for interstitial B, a shallow acceptor which, in the B− state, sits in a tetrahedral lattice site. For interstitial N distortions are large, with a long C-N distance which stabilizes a ŝ∗ orbital that would otherwise be in the conduction band. This orbital has one electron in it and has its greatest amplitude on C; the bonding counterpart has its greatest amplitude on N and is similar to the N lone-pair orbital in amines. The calculations indicate that N is a deep donor and N+ relaxes to the tetrahedral lattice site. Interstitial H is a mid-band-gap donor and is possibly also an acceptor with a high 1.9 eV calculated activation energy barrier to migration. Interstitial H+ is expected to be very mobile, with a migration barrier of 0.1 eV. H− is predicted to be relatively immobile with an activation barrier for migration of 2.5 eV. The mobility of bond-inserted H around B in BH pairs should be high, with a calculated activation energy of 0.13 eV, but for N the comparable process has an activation energy of 2.50 eV. In NH pairs the interstitial H has formed a bond with the radical orbital on the C, so donation would be from the lone-pair orbital on N, which lies deep in the band gap; hence, the donor property is passivated.

The efficiency of far-IR germanium photoconductive detectors can be markedly improved by antireflective coatings. Recently, there has been an effort to develop several micrometer thick, low stress, amorphous carbon films for this purpose. To date, films of no more than 1 to 2 μm have been reported in the literature. In this paper we report the deposition of low stress carbon films which are over 5 μm thick and are effective antireflective coatings at wavelengths of up to Λ = 43 μm. Minimal stress, a requirement for good adhesion, was achieved with a chemical vapor deposition process (CVD) by controlling the hydrocarbon partial pressure (2.2 mTorr) and by doping the carbon film with nitrogen.

Interfacial reactions of Ni/amorphous Si(a-Si) multilayers are studied by means of transmission electron microscopy (TEM) and cross-sectional transmission electron microscopy (XTEM). Transformation from a crystalline to an amorphous structure has been observed in as-deposited Ni/a-Si multilayers with small modulation periods. This phenomenon is suggested to be due to interdiffusion-induced solid state amorphization which is facilitated by the high density of interface in the shorter modulation period multilayers. A thermodynamic and kinetic explanation is given for this phenomenon.

Cu/Al2O3 bilayer samples were produced by vapor deposition and irradiated successively with 150 keV Ar ions up to a dose of 500 dpa. Ion beam mixing effects were studied by 2 Me V He+ Rutherford backscattering spectroscopy (RBS). Concentration depth profiles show the mixing of Cu, Al, and O atoms in the sample. Because of the low mixing efficiency found in this study, Al2O3-dispersion strengthened Cu alloys seem to be good candidates as structural materials in fusion reactors.

We have grown epitaxial thin films of rare-earth hexa-aluminates on basal plane sapphire from liquid precursors. LnAl11O18 (Ln = Gd3+, Nd3+) films form via the reaction of a perovskite intermediate phase and the sapphire substrate according to LnAlO3 + 5Al2O3 = LnAl11O18. Hexa-aluminate thin films with magnetoplumbite (MP) structure grow epitaxially with (0001)mp ‖(0001)s, 〈1120mp‖〈1010〉s orientation relationship. The a-axis of the film is rotated 30°with respect to the substrate. This rotation results in a smaller mismatch (∼1%) between the two oxygen sublattices. Thermodynamic and kinetic arguments pertaining to magnetoplumbite formation for the smaller Gd3+ cation are presented. These epitaxial thin films are likely to have application in higher temperature ion conduction, catalysis, fluorescence, and as laser host.

Epitaxial lead lanthanum zirconate titanate [PLZT(9/50/50)] thin films were fabricated on various single crystal substrates using the spin coating of metallo-organic solutions. The films were heat-treated at 700 °C for 1 h using the direct insertion method. The films were epitaxially grown with (100), (100), and (110) being parallel to the SrTiO3(100), the MgO(100), and the sapphire (0112) substrates, respectively. The epitaxy of the films was investigated using x-ray diffraction, pole figures, rocking curves, and scanning electron microscopy.

Thin films of BaTiO3 deposited on (100)LaAlO3 substrate by metal-organic chemical vapor deposition (MOCVD) are investigated using several electron-optical techniques. Combined high resolution transmission electron microscopy (HRTEM), electron energy loss spectrometry (EELS), and convergent beam electron diffraction (CBED) indicate a substantial influence of lattice strain on the structural and optical characteristics of BaTiO3 films. Spatially resolved EELS and CBED studies indicate that the substrate influence persists up to about 40 nm away from the interface. The changes in the dielectric function of the films, as inferred from spatially resolved EELS, appear to correlate well with internal lattice strain in the films as deduced from convergent beam electron diffraction (CBED).

Titanium carbonitride, TiC0.5N0.5, is synthesized directly by a self-propagating reaction between titanium and carbon in a nitrogen atmosphere. Complete conversion to the carbonitride phase is achieved with the addition of TiN as diluent and with a nitrogen pressure ≥0.6 MPa. Thermodynamic phase-stability calculations and experimental characterizations of quenched samples support a proposed mechanism in which the formation of the carbonitride is a two-step process. The first step involves the formation of the nonstoichiometric carbide, TiC0.5, and is followed by the formation of the product by the incorporation of nitrogen in the defect-structure carbide to form the carbonitride solid solution.

Dispersions of uniform submicron spherical particles consisting of silica cores and yttria coatings, or vice versa, were prepared by a precipitation technique. The overall size of the particles and the thickness of the shells could be varied over a wide range. Such powders were used to form green bodies by sedimentation, centrifugation, or pressure filtration, and the density and the pore size distribution of the resulting solids were evaluated. The green bodies were sintered and the changes in density, phases, and microstructure were followed with temperature. In general, the coated powders exhibited enhanced densification. On processing composite solids at temperatures <1000 °C, the formation of Y2Si2O7 took place, which caused a pronounced shrinkage of the samples. Powders of coated particles having the same silica/yttria ratios sintered at lower temperatures when the shell was composed of silica rather than of yttria. When either silica or yttria were in molar excess in the coated particles, the sintered products had a mixed composition of Y2Si2O7 and the component in excess. By terminating the sintering process before the grain growth started, the solids displayed a well-defined microstructure with a uniform distribution of areas of one phase in the matrix of the matter in excess. This property was mainly due to the uniformity of initial powders in terms of the particle size and the coating.

A combined experimental and theoretical investigation of the sedimentation of unstable colloidal ceramic suspensions has been performed. Suspensions containing submicron-sized α-Al2O3 particles were prepared at various pH values in order to modify suspension stability. Particle volume fraction during sedimentation was determined as a function of position and time by gamma-ray densitometry. A population balance model was developed to account for various coagulation and decoagulation mechanisms that affect sedimentation behavior in flocculating suspensions. Model predictions were then compared with experimental measurements, in order to establish the validity of the theoretical model.

Ni(II)- and Co(II)-bearing ferrites with different levels of metal substitution have been studied for CO2 decomposition. Ni2+ and Co2+ have been substituted for Fe2+ or Fe3+ in magnetite with the spinel type of crystal structure up to 14% and 26% for the mole ratio of Ni2+ and Co2+ to the total Fe contents, respectively. The metal substitution was corroborated by Mössbauer spectroscopy and XRD studies. They were activated in a flow of H2 gas to form oxygen-deficient ferrites with the spinel structure retained. The oxygen-deficient M(II)-bearing ferrites have been found to show high reactivity toward CO2 decomposition to carbon at 300 °C. The reactivity increased with the level of metal substitution and activation. The oxygens of CO2 were incorporated into the spinel structure and carbon was deposited on the surface of the ferrites. The deposited carbon was visible on dissolution of the ferrites used. The rate of decomposition on H2-activated Ni(II)-bearing ferrite with the mole ratio of 14% was 30 times as high as that of H2-activated magnetite.

Oxyreduction studies of mixed Ce/Pr oxides have been carried out. Temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), and temperature-programmed oxidation (TPO) were used to study the uptake and release of the oxygen. Large amounts of oxygen, exceeding those in ceria, are accessible in the mixed metal oxides at moderate temperatures. The addition of small amounts of noble metals to the mixed oxides shifts the accessibility of the “stored” oxygen to still lower temperatures with the effect of Pd being more pronounced than that of Pt. In a sample containing 45 mol % ceria and 55 mol % praseodymia, a small addition of Pd (0.24 mol %) was found to lower the reduction temperature by more than 100 °C. The addition of Pt had a lesser effect. Similarly, in pure praseodymia (Pr6O11) Pd influences the reduction much more strongly than Pt. In the mixed samples, whether doped with a noble metal or not, the whole oxyreduction effect can be accounted for by the change in oxidation state of the praseodymium ions solely. This notwithstanding, the reduction of the mixed oxides, without noble metals or doped by Pt, is more facile than that of praseodymia. Only the incorporation of Pd makes the reduction of praseodymia proceed at a temperature below that registered for a mixed ceriapraseodymia sample.

We report scanning tunneling microscope images of gold-coated fracture surfaces of soda lime glass and fused silica in the mirror region. The scans show a variety of nanometer scale features that are attributed to fracture phenomena at this scale. We find considerable similarity to the structures observed in regions of extensive crack branching (e.g., “mist”). The density of these features increases as one progresses away from the crack origin toward the mirror-mist boundary. Comparisons are made between soda lime glass and fused silica, revealing differences in the local deformation behavior of these two materials. Self-similarity of the observed structures is probed by measurements of the fractal dimension, Df, of the surfaces created in soda lime glass near the mirror-mist boundary, where we observe 2.17 > Df > 2.40.

Densification kinetics and mechanism of a binary borosilicate glass composite, containing low-softening borosilicate (BSG) and high-softening high silica (HSG) glasses, have been studied. Apparent activation energy of densification varies from 200 to 400 kJ/mol, and decreases with increasing BSG content at a given densification factor. At a given BSG content, the activation energy of densification initially remains relatively unchanged with increasing densification factor (DF), but increases with densification when DF reaches a critical value (DF∗). Moreover, the value of DF∗ increases with increasing BSG content. From the activation energy estimates of densification, it is concluded that the predominant densification mechanism for BSG ≥ 30 vol. % with DF < DF∗ is viscous flow of low-softening BSG. For BSG ≥ 30 vol. % with DF < DF∗ and BSG ⋚ 20 vol. % with all DF investigated, the activation energies are within the range governed by viscous flow of both BSG and HSG, indicating that the densification is controlled by viscous flow of a new glass with a composition between BSG and HSG. The latter evidence stems from the microstructural observation that as sintering proceeds, the HSG particle undergoes an extensive dissolution process.

CdTe microcrystallites were precipitated in 57.8CdO · 19.7SiO2 · 19.0B2O3 · 3.5Al2O3 glasses doped with 5.0 mol % CdTe. The microcrystallite size increased linearly with t1/3 (t: heat-treatment time), indicating diffusion-controlled growth mechanism, where the estimated activation energy for diffusion was 542 kJ/mol. The linear increase in the band gap energy with l/r2 (r: the crystallite radius) suggested the quantum size effect of the CdTe microcrystallites.

The mechanical properties of the interfaces in an Al2O3 fiber reinforced β-21S Ti alloy have been evaluated by using fiber pushout tests. The Al2O3 fibers were coated with a refractory metal and Y2O3 which served as a diffusion barrier during the HIPing used to produce the metal matrix composites. By doing fiber pushout tests, the interfacial fracture was found to occur at the interface between the refractory metal and the Y2O3. The interfacial shear strength and interfacial frictional stress were measured to be 323 and 312 ± 2 MPa, respectively. The interfacial frictional stress, which is due to asperity interlocking during the fiber sliding, was correlated to the surface roughness of the coated Al2O3 fiber obtained with the aid of an atomic force microscope. The measured surface roughness of 18.8 ± 2.2 nm was related to the frictional stress through Hutchinson's model.9 The frictional coefficient between the Al2O3 fiber and the Ti matrix is calculated to be 0.32 ± 0.02.

Effects of thermal cycling in a reducing (deuterium) atmosphere on the structure and chemistry of Cr/Cu/Cr/polyimide (PI)/Si and Au/Cu/Ti/polyimide (PI)/Si multilayer systems have been studied. In the Cr/PI system the interface between the Cr and PI was sharp and distinct in the as-deposited state, and after the anneal in the reducing atmosphere. Tensile cracks through the Cr/Cu/Cr layers were found after annealing and are the result of thermal stresses. No evidence for significant diffusion of Cr into the PI was found. In the Ti/PI system, the interface between the Ti and PI was sharp in the as-deposited state. After annealing in vacuum and in the reducing environment, regions of the interface between the Ti layer and the PI were converted to an oxide, Ti5O9. Annealing in the deuterium environment also caused delamination of the Ti film from the PI and blistering of the metal in the sample interior. No significant diffusion of the Ti into the PI was detected. In both systems, the metal in contact with the PI acted as a barrier to the diffusion of Cu into the PI.

The statistics of random cellular patterns are analyzed in cross sections of low-density microcellular materials. Agreement is found with a variety of topological relations previously found for other networks, namely Lewis's law and Aboav's law. To investigate three-dimensional packing effects, experiments are performed on compressed polystyrene shot material, the resulting networks of which are subsequently analyzed in cross section. Implications for material properties and stability are discussed.