A Ni-P solid-solution phase was obtained by quenching from the melt under a pressure of 4.5 GPa. It was considered as a metastable high-pressure phase. Metastable phases with the same composition as the melt, such as supersaturated solid solutions and amorphous phases, are easily prepared using a high pressure quenching method.

Amorphous aluminosilicate gel powders have been subjected to carbothermal reduction and nitridation reaction at high temperature (1673 K). The influence of Al2O3 content in the gel powder on the nature and structure of the product phases has been examined. Between 5% and 9% Al2O3 in the gel powder, it is found that only β-SiAION is formed as the product of CTR/N reaction.

BaTiO3 doped 90V2O5−10Bi2O3 (VB) oxide glasses show a larger dielectric constant (102-104) compared to that of the base glass VB (∼102). The VB glass with 15 wt.% BaTiO3 shows the largest dielectric constant, and all the glasses show a Debye-type dielectric relaxation behavior. The increase in dielectric constant appears to be mainly due to the formation of microcrystalline clusters of BaTiO3 (1.8–8 μm, depending on the BaTiO3 concentration present in the base glass). Other than the dilution effect with BaTiO3, the glass-former oxide Bi2O3 also influences the dielectric behavior of BaTiO3 doped VB glasses.

Systematic studies have been performed on 1000 Å YBa2Cu3O7−δ films produced by the BaF2 process and annealed in an oxygen partial pressure (Po2) range from 740 Torr to 10 mTorr as well as a temperature range from 600 to 1050 °C. The results show that while high quality films can be annealed in a wide range of oxygen partial pressure, they have different characteristics. In general, crystalline quality and Tc are optimized at high Po2 and high annealing temperature, while strong flux pinning and low normal state resistivity are achieved at lower values of both variables. Under optimized low Po2 conditions, an ion channeling Xmin of 6% is obtained on films as thick as 5000 Å. This study will serve as a useful guide to tailoring film properties to the application at hand.

Single crystals of YBa2Cu3O7−x (Y123) were grown by a modified top-seeded crystal pulling method using a BaO-CuO solution with the solid Y2BaCuO5 (Y211) as a solute in an yttria crucible [the so-called solute-rich liquid crystal pulling (SRL-CP) method] under 2% oxygen partial pressure atmosphere [P(O2) = 0.02 atm]. According to the pseudo-binary phase diagrams of Lee and Lee,1 the temperature of Y123 crystal growth was expected to be lower for 0.02 atm oxygen pressure than for 0.21 atm oxygen pressure. The single crystals grown under P(O2) = 0.02 atm and cooled under the same atmosphere after the separation of crystal from a solution had twins near the microcracks on the crystal surface. On the other hand, the single crystals grown under P(O2) = 0.02 atm and cooled under pure nitrogen atmosphere (6N) showed no twin structure. These results indicate that twins did not form during crystal growth but formed due to tetragonal-orthorhombic transition as a consequence of oxygenation at cooling under low oxygen partial pressure.

The formation of BaCeO3 and its effects on microstructure were studied in sintered/melt-textured Y-Ba-Cu-O oxides containing 5 wt. % CeO2 and various amounts of Y2Ba1Cu1O5. The added CeO2 was converted to fine particles of BaCeO3 near 930 °C, which is the conventional sintering temperature for Y-Ba–Cu-O. Y2Ba1Cu1O5 and CuO are formed as by-products of the reaction between CeO2 and Y1Ba2Cu3O7−y phase. The CeO2 addition reduced the particle size of Y2Ba1Cu1O5 which was trapped in the Y1Ba2Cu3O7−y matrix after the melt-texture growth. During the peritectic decomposition stage of Y1Ba2Cu3O7−y phase into Y2Ba1Cu1O5 and liquid phase, the morphology of the decomposed Y2Ba1Cu1O5 was changed from a blocky shape in the undoped sample to an acicular shape of high anisotropy in the CeO2-added sample. The formation of the highly anisotropic Y2Ba1Cu1O5 particles appears to be responsible for the refinement of Y2Ba1Cu1O5 particle after the melt-texture processing.

Multilayer thin films of SrCuO2/(Sr0.5Ca0.5)CuO2 with an infinite-layer structure have been prepared on (100) SrTiO3 single crystals by multitarget rf magnetron sputtering. The structural analyses of the multilayers were carried out by means of x-ray diffraction (XRD), secondary ion-mass-spectroscopy (SIMS), and transmission electron microscopy (TEM). Heteroepitaxial growth of the SrCuO2 and (Sr0.5Ca0.5)CuO2 layers was confirmed to be with the c-axis perpendicular to the (100) SrTiO3 surface. The XRD and SIMS measurements revealed that the compositional modulations of the multilayer films were successfully constructed as we designed. However, in the TEM images, there existed planar dislocations parallel to the ac- and bc-planes, which went across the boundaries of the SrCuO2 and (Sr0.5Ca0.5)CuO2 layers. The resistivity of the multilayer films showed semiconductor-like behavior with temperature, and there was no relation between electric properties and modulation wavelength.

Bi-Sr-Ca-Cu-O phases provide continuous manufacturing of tapes in long lengths using conventional techniques. Thick films of the BPSCCO 2223 phase [(Bi, Pb)2Sr2Ca2Cu3O10+x] were successfully prepared on Ag tapes by combining the processes of screen-printing with organic binders, cold deformation, and sintering.1 Technical and economical studies revealed that these processes have optimal properties for conductor fabrication. The effect of atmosphere and powder composition on the formation of the 2223 superconductor phase was studied on two different composites: BPSCCO/Ag (open system) and Ag/BPSCCO/Ag (closed system). For the open system, both the evaporation of lead had to be avoided and the presence of additional “catalytic” Ag grains within the layer is necessary to promote the reaction of 2223 phase. Critical current densities jc of 6–12 ± 103 A/cm2 (77 K, O T) were achieved in samples of the closed system.

Aluminum ions may exist in one of several different types of polynuclear species depending upon the degree to which it is hydrolyzed. The hydrolysis of aluminum can be explained by a metastable equilibrium among Al(H2O)3+6, Al(OH)(H2O)2+5, Al13O4(OH)24(H2O)7+12, and an oligomer. We have made small angle x-ray scattering and 27Al NMR measurements on 0.3 M aluminum chloride solutions over a range of OH/Al ratios. 27Al NMR shows two sharp peaks corresponding to the monomer Al(H2O)3+6 and the tetrahedrally coordinated aluminum in Al13O4(OH)24(H2O)7+12, and a broad peak due to the octahedrally coordinated aluminum in the oligomer. The observed radius of gyration (Rg) of the species in solution increases from 3.0 to 3.6 A, and the intensity at zero angle (which is proportional to the weight average molecular weight of the species) also increases as the OH/Al ratio increases from 1.0 to 2.2. The oligomer has an Rg of approximately 3.3 A, a hydrolysis ratio close to 2.0, and may be a six-membered ring with a structure similar to that of a gibbsite layer.

A complex-shaped TiAl turbine rotor has been uniformly aluminized by a metal-organic chemical vapor deposition under reduced pressure (RPMOCVD), and a thick TiAl3 layer, which affects the oxidation resistance, can be formed on the surface by subsequent heat treatment. The oxidation resistance has been studied with an oxidation test at 1173 K for 760 ks in static air. The microstructure has been investigated by SEM, EPMA, AES, and XRD. A heat treatment at above 933 K, which is the melting point of Al, is required to enhance the oxidation resistance of TiAl. With increasing the surface roughness of TiAl, the formation of TiAl3 increases, and consequently the oxidation resistance is more improved.

The effect of alumina on densification of the binary borosilicate glass composite, containing low-softening borosilicate glass (BSG) and high-softening high silica (HSG) glass, has been investigated. It is found that with a small amount of alumina, 2-10 vol. %, present as a dopant in the binary glass mixture of BSG and HSG, both densification and densification rate are significantly reduced, but the activation energy of densification at a given densification is dramatically increased. However, no significant change in densification behavior with increasing alumina content from 2 to 10 vol. % is observed. These results are attributed to a chemical reaction taking place at the interface of alumina/BSG, forming a reaction layer adjacent to alumina. Since the composition of the reaction layer is known to be rich in aluminum and alkali ions and poor in silicon, the alkali ions content in BSG is continuously decreased during sintering. Accordingly, the resultant loss of alkali ions from BSG causes a rise in viscosity of BSG, thus slowing down the densification kinetics and increasing the activation energy of densification.

An important, rather novel procedure for the synthesis of submicron crystalline multicomponent oxide ceramic powders has been studied. The synthesis of CuFe2O4 powder, a ferrite material, has been used as a model system for understanding the synthesis process. The effect of the fuel content, powder packing, and surface heat loss has been investigated in terms of the maximum reaction temperature and reaction period, phase formation, and particle size and morphology. It has been shown that the maximum temperature and reaction period can be tailored to produce different phases. The submicron features of the synthesized powders are indicated by the large surface area values obtained from BET measurement.

NaZr2P3O12 (NZP) is emerging as an important family of a large number of isostractural compounds in which several members have demonstrated very low thermal expansion characteristics. Ba1+xZr4P6−2xSi2xO24 and Sr1+xZr4P6−2xSi2xO24 crystalline solutions are two such systems belonging to the NZP family. Here, we report the bulk thermal expansion and axial thermal expansion behavior of various compositions in these systems. The low expansion behavior of these materials is attributed to their unique crystal structure, which is framework open structure, and can accommodate numerous ionic substitutions at various lattice sites.

Thin film coatings of (Ca0.6, Mg0.4)Zr4(PO4)6 (CMZP) on Si3N4, and SiC substrates, including porous SiC used in ceramic filters, were investigated using sol-gel and dip coating techniques. The coating thickness, ranging from 1 to 5 μm, was found to vary with the selected precursors and their concentrations in the solution. When applied to Si3N4 and SiC, CMZP coatings exhibit good thermal shock resistance and greatly improved alkali corrosion resistance. For porous silicon carbide, homogeneous, crack-free coatings were formed on both the outer surface and the interior sections of the pore walls. The CMZP coatings on Si3N4 and SiC exhibit good thermal shock resistance. The CMZP coating greatly improved the alkali corrosion resistance of Si3N4 and SiC.

The decomposition of congruent lithium niobate (LN) crystals proceeds by surface nucleation and growth of LiNb3O8 precipitates which exhibit an epitaxial orientation relationship. The same orientation relationship is observed on x-, y-, and z-cut LN substrates. The epitaxy arises from similarities between the two crystal structures and provides for an essentially continuous oxygen-ion framework from parent to product. On y-cut LN, the precipitates have a well-defined habit plane, and the interfacial misfit between the two structures is accommodated by a rectangular grid of misfit dislocations. The density, geometry, and imaging behavior of the misfit dislocations suggest that their Burgers vectors serve to accommodate the disregistry in the oxygen-ion framework. Based on these observations, it is concluded that the mechanism of formation of LiNb3O8 consists of preferential nucleation on the surface and subsequent growth, possibly by counterdiffusion of cations in a closed system where the oxygen-ion framework remains essentially fixed in space.

The microstructural development of Ti: LiNbO3 optical waveguides, as a function of annealing time and temperature, was studied by x-ray diffraction, scanning and transmission electron microscopy, and Auger electron spectroscopy. The microstructure evolves in three major stages: oxidation, precipitation and abnormal grain growth, and interdiffusion. The deposited Ti film is oxidized at low temperatures through a series of intermediate TiOx phases until complete oxidation to rutile TiO2 occurs at ∼500 °C. At intermediate temperatures, 500-800 °C, epitaxial precipitates of LiNb3O8 are formed at the rutile/LiNbO3 interface. At this stage abnormal grain growth occurs in the rutile film, causing multivariant epitaxy where all of the grains have a single orientation relationship to the substrate. Subsequent interdiffusion between TiO2 and LiNb3O8 produces a solid solution with the rutile structure which, at these temperatures, appears to coexist in equilibrium with the underlying lithium niobate substrate. This rutile solid solution serves as the source of Ti in the final stage of interdiffusion, which occurs only at higher temperatures (≳ 1000 °C), and leads to consumption of the rutile layer by the substrate. Structural models are discussed for epitaxial grain growth and interdiffusion.

The morphology and the growth mechanism of lithium borate crystals from the vitreous state have been studied for various compositions, X = B/(Li + B), from 0.62 to 0.75. Crystalline phases and morphology of grown crystals varied with the composition. Octahedral and/or spherical Li2B4O7 crystals are seen in the specimen with X = 0.62, 0.64, 0.67, and 0.68. The spherical crystal is composed of an octahedral core and fibrous crystals. The size of the core varied with the composition of the starting glass, X. The fibrous crystal growth is supposed to arise from the morphological instability due to the compositional variation caused by the solute pileup at the growth interface.

Structural defects occurring on the {311} planes of single crystal silicon have been observed near the bottom oxide corner in silicon-on-insulator structures formed by selective epitaxial growth. These {311} defects exhibit a preferential orientation and are clustered near the silicon/silicon dioxide interface. This new observation provides an opportunity to study the mechanism of {311} defect generation in a system with discernible microstructure and stress state. High resolution electron microscopy combined with analytical and numerical three-dimensional stress modeling are used to show the dependence of these {311} defects on the local stress field, and to establish their origin in terms of a homogeneous dislocation nucleation model.

Traditional CVD phase diagrams, which neglect the depletion effects in a hot wall reactor and assume the gaseous species concentrations at the substrate are the same as input concentrations, are at best valid for a cold wall reactor. Due to the constant change of gaseous species concentration along the length of the reactor, traditional CVD phase diagrams do not accurately predict the phases in the deposit on the substrate in a hot wall CVD system. In this paper, a new approach to calculate the local equilibrium CVD phase diagrams at the substrate is presented by coupling the depletion effects in a hot wall reactor to the equilibrium thermodynamic computer codes solgasmix-pv. The deposition of SiC using the gas system of methyltrichlorosilane (MTS)-hydrogen (H2) under low pressure was chosen for this study. Differences between the new CVD phase diagrams and the traditional phase diagrams for this gas system are discussed. The calculated CVD phase diagrams are also compared with the experimental data both from our own experiment and from the literature. The local equilibrium phase diagrams predicted the deposition of a single phase of SiC much better than those without the consideration of the depletion effects. The experimental regions for depositing single phase SiC are larger than the calculated local phase diagrams. This is attributed to the higher linear velocity of the gas flux under low pressure and the polarity of the Si carrying intermediate species.

In this study, nanoindentation is used to determine Young's modulus of chemically vapor deposited films consisting of silicon carbide, silicon nitride, boron carbide, boron nitride, and silicon dioxide. Diethylsilane and ditertiarybutylsilane were used as precursors in the synthesis of the silicon-based material, while triethylamine borane complex was used for the boron-based material. The modulus of these films was observed to be dependent on the processing conditions and resulting composition of the deposits. For the silicon carbide, silicon nitride, boron carbide, and boron nitride films, the carbon content in the films was observed to increase significantly with higher deposition temperatures, resulting in a corresponding decrease in values of Young's modulus. The composition of the silicon dioxide films was near stoichiometry over the investigated deposition temperature range (375–475 °C) with correspondingly small variations in the micromechanical properties. Subsequent annealing of these oxide films resulted in a significant increase in the values of Young's modulus due to hydrogen and moisture removal.