Grain growth behavior in reactive spray deposited Al–Mg–Mn alloy 5083 and 5083 + Zr was quantitatively studied at 500, 530, and 560 °C. Results show that reactive spray deposited 5083 processed using N2–5% O2, in which no significant volume fraction of oxide particles was found, experienced significant grain growth when annealed at 500, 530, and 560 °C following recrystallization. On the other hand, reactive spray deposited 5083 atomized with N2–10% O2 and 5083 + Zr atomized with N2–5% O2 exhibited very slow grain growth below 530 °C and limited grain growth at 560 °C. This behavior is attributed to the retardation effect of the secondary phase particles that were formed in these alloys.

(200)-oriented Pt thin films were deposited on SiO2/Si substrates by dc magnetron sputtering using Ar/O2 gas mixtures. Oxygen incorporation into Pt films changed deposition rate, resistivity, stress, and preferred orientation of the films. Increase in film resistivity and decrease in tensile stress were presumed to be the results of the incorporated oxygen into grain boundaries, while the change of preferred orientation resulted from the oxygen incorporation into the Pt lattice. The preferential growth of (200) planes with less total strain energy from the incorporated oxygen resulted in strong (200) preferred orientation in Pt films.

The densification of Si3N4 with nano-sized sintering aids that were in situ incorporated by a combustion process was studied in comparison with that of sintering aids mixed by ball milling. The combustion process directly produces amorphous and nano-sized Y–Al oxides within the Si3N4 powder. X-ray diffraction results indicate that amorphous Y–Al oxides begin to crystallize into Y3Al5O12 at about 600 °C. Additionally the nano-sized sintering aids are more homogeneously distributed and thereby promote the formation of eutectic melts at lower temperatures during liquid-phase sintering. Therefore, the densification process of Si3N4 during liquid-phase sintering is strongly accelerated. The microstructure of as-sintered parts from combusted powder seems more dense and homogeneous.

Early-stage processes involving the polymerization of zirconium species in aqueous solutions at elevated temperatures (∼100 °C) as well as colloid formation were studied. Small-angle x-ray scattering (SAXS) data were analyzed via Guinier, “longrods,” and Porod plots to determine particle growth kinetics and morphology. Our SAXS data suggest that zirconium tetramers and octamers polymerize into larger clusters and elongated-rod-(or needle)-shaped primary particles, which have a length of a few nanometers and a radius of gyration of cross section between 4 and 5 Å. Cube-shaped particles are aggregates of the needlelike primary particles. The transition from zirconium tetramer to a colloidal sol particle follows a mass-fractal growth (1 < fractal dimension, D <3)

Transmission electron microscopy has shown that the grain size of sol-gel-prepared lanthanum-modified lead titanate films increases from ∼100 to ∼1 μm when the excess of PbO in the precursor solution is reduced from 20 to 10 mol%. Switchable polarization is higher in the films with a smaller grain size. Profilometry and the temperature dependence of the dielectric permittivity indicate that films are tensile stressed by the substrate. The grain-size effect on polarization switching is explainedby taking into account this tensile stress, which is thought to induce some a-domain orientation and 90° domain wall clamping in the grains attached to the substrate.

Rare-earth aluminates, LnAlO3 (Ln = Dy, Er, Gd, La, Nd, Pr, Sm, and Y) were prepared using the mixed oxide method, and their microwave dielectric properties were examined at X-band. Most rare-earth aluminates have suitable permittivities and quality factors for applications as dielectric resonators, but a modification of τf is necessary due to the coefficient's large negative value. When considering dielectric properties and lattice matching, YalO3 rather than LaAlO3, was suggested as a promising substrate material for microstrip antennas utilizing high-temperature superconductor thin films. Rare-earth aluminates with a rhombohedral structure exhibited larger permittivities than those with an orthorhombic structure. This difference was attributed to the difference in ionic size and coordination number. It was demonstrated that a nonzero magnetic susceptibility of rare-earth aluminates has an adverse effect on their quality factor. An abrupt variation in the temperature coefficient of permittivity was discussed in terms of oxygen octrahedra tilting.

Oxidation resistance of ceramic matrix composites (CMC) of SiC reinforced with C fibers (C/SiC) can be improved by filling the residual porosity. The aim of this work was to design and analyze a dipping infiltration process under ambient conditions (1 atm pressure and room temperature) with silica sol-gel solutions prepared from tetraethyl orthosilicate. Different substrates and solutions have been studied. Thermal treatments, i.e., curing or sintering between infiltrations, increase the efficiency of the process since the densification of infiltrated silica opens up the remaining porosity. Increasing viscosity and/or concentration of the solution lead to greater weight gains. Weight gains are higher in the initial stages of the process because larger diameter porosity remains unfilled. As the process advances, the average pore size decreases, and only the lower viscosity solution can enter the residual porosity.

Polycrystalline Y2O3/ZrO2 superlattice thin films were deposited using opposedcathode reactive magnetron sputtering. Pulsed direct-current power was used to eliminate arcing on the metallic targets. Radio-frequency power was applied to the substrates to achieve ion bombardment of the growing film. In order to reproducibly deposit at high rates in Ar–O2 mixtures, the Y target voltage was used to indirectly feedback-control the O2 partial pressure. Deposition rates as high as ∼70% of the pure metal rates were achieved, typically 3.5 μm/h. Superlattices with periods ranging from 2.6 to 95 nm were deposited. Y2O3 layer thicknesses were either 75% or 50% of the superlattice period. X-ray diffraction and transmission electron microscopy studies showed well-defined superlattice layers. The ZrO2 layers exhibited the high-temperature cubic-fluorite structure, which was epitaxially stabilized by the cubic Y2O3 layers, for thicknesses ≤7 nm. The equilibrium monoclinic structure was observed for thicker ZrO2 layers. Nanoindentation hardnesses ranged from 11.1 to 14.5 GPa with little dependence on period. The hardness results are discussed in terms of current superlattice hardening theories.

Nickel is a commonly used wetting agent in alloyed Au–Ge ohmic contacts to n-GaAs, resulting in uniformity improvements to the morphology and contact resistance. In order to study the role of Ni in Ni–Ge–Au alloys, we have fabricated samples with varying Ni content and characterized them using electron microbeam techniques. Our data indicate the amount of Ni in the alloy affects the microstructure and composition, the morphology of the metal/GaAs interface, and the amount of GaAs consumed during the alloy reaction. Also, the dopant distribution into the GaAs is heterogeneous depending on the alloy microstructure.

The feasibility of the acetylacetonate-Ti isopropoxide complex as a new precursor for synthesis of Ti-based perovskite particles under hydrothermal conditions has been demonstrated. Perovskite powders including BaTiO3, PbTiO3, PZT, PLZT, and SrTiO3 were prepared by reacting the acetylacetonate-modified Ti precursor in metal acetate aqueous salt solution under hydrothermal conditions. Synthesis parameters including reaction time and temperature, feedstock concentration, nd reaction medium significantly influence particle characteristics of the hydrothermally derived erovskite powders. It is proposed that use of the acetylacetonate-modified Ti precursor promotes ntimate mixing among multicomponent reacting species at the molecular level and promotes article formation through a dissolution/recrystallization mechanism.

Subsolidus equilibria in air in the La2O3–Ga2O3–NiO system were studied with the aim of obtaining information on possible interactions between a LaGaO3-based solid electrolyte and NiO during preparation of the anode in solid oxide fuel cells (SOFC). No ternary compound was found. The tie lines are between La4Ga2O7 and La2NiO4, LaGaO3 and La2NiO4, LaGaO3 and NiO, and LaGaO3 and NiGa2O4.

Composites containing micron-sized lead zirconate titanate and nanometer-sized lead sulfide in a glass matrix were prepared using a sol-gel technique. The PbS size ranged from 3.5 to 15.3 nm. It was possible to pole some of these nanocomposites. The measured values of saturation polarization, remanent polarization, and coercive field showed an increase as the PbS particle size was enhanced. The composites exhibited improvement in the piezoelectric and pyroelectric behavior as compared to that of the base glass-ceramic.

The reaction kinetics in vapor-deposited indium/amorphous-selenium (a-Se) multilayer thin films were studied using differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electron microscopy (TEM). A number of reactions were observed upon heating with characteristic temperatures which were found to be independent of the multilayer modulation wavelength. The initial interface reaction between In and a-Se is the formation of an In2Se phase. Kinetic analyses of the In2Se formation process combined with TEM observations indicated that interface reaction is characterized by the two-dimensional growth of pre-existing In2Se regions formed during deposition to impingement in the plane of the original In/a-Se interface. The change of the density of In2Se grains with temperature was analyzed in terms of the derived kinetic parameters, which is consistent with TEM observations and the heat release measurements.

A nanocrystalline PbTiO3 particle/organic hybrid was synthesized through hydrolysis and polymerization of metalorganic compounds below 100 °C. The PbTiO3 precursor was synthesized from lead methacrylate and titanium isopropoxide. The formation of a Pb–Ti complex alkoxide was confirmed by H and Pb nuclear magnetic resonance spectroscopy. Hydrolyzed Pb–Ti alkoxide was polymerized, yielding the PbTiO3 particles/oligomer hybrid. The organic matrix included nano-sized crystalline particles, depending on the hydrolysis conditions. The nanocrystalline particles were identified to be lead titanate by electron diffraction and energy-dispersive x-ray analysis. The dielectric constant of the nanometer-sized PbTiO3/oligomer hybrid was 5.2 at 10 kHz.

The influence of ternary additions Cr, Fe, Mn, Ni, Zr, Nb, Mo, Hf, Ta, Si, Ga, Ge, In, and Sb, as well as the anti-site defects of both Ti and Al, on lattice parameters of TiAl were studied by the first principles electronic structure calculations with a discrete variational cluster method. The results of the calculation show that the effect of ternary additions on the distortion of TiAl lattice varies with the substitution behavior of the individual alloying element involved. The addition of alloying elements in TiAl causes a change in the electronic structure and the density of states of the system and results in variation of the bond strength between the atoms. The total and partial density of states (DOS) of binary TiAl and of ternary TiAl–M, M = Cr, Zr, and Sb, etc., were comparatively examined. The relationship between the DOS and the bond strength is discussed. The present work suggests that the origin of the lattice distortion of the ternary TiAl–M systems lies in the variation of the electronic structure.

The effect of different cations in the anatase–rutile phase transition temperatures for titania prepared by the sol-gel method was studied. The metal dopants were chosen from different periods and groups of the periodic table to see the role played by the electronic configuration, the oxidizing state, the atomic size, etc. on these temperature modifications. Linear relationships between the anatase–rutile phase transition temperatures and the ionic radii for alkali metal, alkaline earth metal, and group 3 and 13 elements were obtained. For elements of the period 4, there was not such a defined tendency; for most of them the modification of the phase transition temperature was too small. The cations used were Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Y3+, La3+, Er3+, Ti4+, Co2+, Ni2+, Cu2+, and Zn2+. In all cases the dopant's concentration was 2 mol% with respect to titanium, and the same anion (nitrate) was used for all salts. A variation of more than 330 °C in the anatase–rutile phase transition temperatures was obtained by using these dopants. The transition temperatures from amorphous to anatase and from anatase to rutile phases were obtained from the x-ray diffractograms.

Nanocrystalline titanium dioxide was prepared via aerosol pyrolysis of titanium alkoxide precursor at 200–580 °C in air and in nitrogen atmospheres. Powders were characterized by x-ray diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller analysis, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, x-ray fluorescence, Raman and infrared spectroscopy, and Berner-type low-pressure impactor. The anatase phase transition was initiated at 500 °C in nitrogen and at 580 °C in air. Under other conditions amorphous powders were observed and transformed to nanocrystalline TiO2 via thermal postannealing. In air, smooth and spherical particles with 2–4-μm diameter were formed with an as-expected tendency to convert to rutile in the thermal postannealings. In nitrogen, a fraction of the titanium tetrabutoxide precursor evaporated and formed ultrafine particles via the gas-to-particle conversion. At 500 °C thermally stable anatase phase was formed in nitrogen. A specific surface area as high as 280 m2 g−1 was observed for an as-prepared powder.

Powder metallurgy was used to fabricate fully dense, unreacted composites consisting of a copper matrix containing 50–60 vol% ZrW2O8 particles with negative thermal expansion. Upon cycling between 25 and 300 °C, the composites showed coefficients of thermal expansion varying rapidly with temperature and significantly larger than predicted from theory. The anomalously large expansion on heating and contraction on cooling are attributed to the volume change associated with the allotropic transformation of ZrW2O8 between its high-pressure γ-phase and its low-pressure α- or β-phases. Based on calorimetry and diffraction experiments and on simple stress estimations, this allotropic transformation is shown to result from the hydrostatic thermal stresses in the particles due to the thermal expansion mismatch between matrix and reinforcement.

Among the oxides, Cr2O3 exhibits the highest hardness value and a low coefficient of friction. These properties make chromium oxide an excellent coating material for tribological applications. Cr2O3 thin films were deposited by radio-frequency reactive magnetron sputtering at substrate temperature in the range 363–593 K. The hardness and elastic modulus of the films were measured by two complementary nanoindentation techniques to investigate the influences of the substrate temperature and the oxygen content in the sputtering gas. While the continuous stiffness data method provides information throughout the whole film thickness, nanoindentation combined with scanning force microscopy of the residual imprints allows visualization of pileup, cracking, and delamination from the substrate. Hardness values up to 32 GPa were obtained for substrate temperatures exceeding 500 K and oxygen contents between 15% and 25% of the total gas pressure. The films, obtained with these deposition conditions, showed good adhesion to silicon substrates.

(1–x)PMN–xPT[PMN, Pb(Mg1/3Nb2/3)O3; PT, PbTiO3] system ferroelectric ceramics with x = 0.30, 0.33, 0.35, and 0.38 were synthesized by the columbite precursor method. Their structure and dielectric behavior were investigated. X-ray diffraction results demonstrate that no two-phase region is presented, but a quasi-cubic to tetragonal phase boundary lies between x = 0.30 and 0.33. Examination of the dielectric behavior reveals that the transformation from relaxor to normal ferroelectric behavior across the morphotropic phase boundary (MPB) is successive and continuous. It is suggested that x 4 0.30 to 0.33 is the composition of MPB for the PMN–PT system. The MPB is also a boundary for the PMN–PT system to transform from relaxor to normal ferroelectrics.