The formation of barium monomolybdate (BaMoO4) in inequimolar powder mixtures of BaCO3 and MoO3 was examined under isothermal and nonisothermal conditions upon heating in air at 25–1200 °C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO2) to the occurrence of the formation reaction was evident. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The x-t and x-T data thus obtained were processed using a well-established mathematical apparatus and methods to characterize the nature of the reaction rate-determining step and derive isothermal and nonisothermal kinetic parameters (rate constant, frequency factor, reaction order, and activation energy). Moreover, the reaction mixture quenched at various temperatures (450–575 °C) in the reaction course was analyzed by various spectroscopic (x-ray diffractometry, infrared spectroscopy, and laser Raman spectroscopy) and microscopic (scanning electron microscopy and x-ray energy dispersive spectroscopy) techniques for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of MoO3 species through the product layer (BaMoO4), which was implied to form on the barium carbonate particles. The nonisothermally determined activation energy (156 kJ/mol) was found to be close to the isothermally determined one (164–166 kJ/mol)

Spindlelike, rodlike, starlike, and spherical antimony sulfide (Sb2S3) microcrystallites have successfully been synthesized via a sonochemical method at room temperature. The x-ray diffraction pattern analysis based on the Rietveld method demonstrates that ultrasound can convert the structure of Sb2S3 from amorphous phase to crystalline phase. The crystallinity and morphology of Sb2S3 particles can be modified by using different solvents or solutions. It is found that the spindlelike and starlike particles result from the aggregation of nanoparticles while the rodlike particles arise from epitaxial growth. Due to the quantum confinement effect of charge carriers in small microcrystalline volumes, the characteristic peaks in the optical absorption spectrum of the synthesized 0.001 M Sb2S3 (<100 nm) colloidal solutions are blue-shifted by about 500 nm as compared to the bulk band gaps of Sb2S3.

A method for determining the stress–strain relationship of a material from hardness values H obtained from cone indentation tests with various apical angles is presented. The materials studied were assumed to exhibit power-law hardening. As a result, the properties of importance are the Young's modulus E, yield strength Y, and the work-hardening exponent n. Previous work [W.C. Oliver and G.M. Pharr, J. Mater. Res. 7, 1564 (1992)] showed that E can be determined from initial force–displacement data collected while unloading the indenter from the material. Consequently, the properties that need to be determined are Y and n. Dimensional analysis was used to generalize H/E so that it was a function of Y/E and n [Y-T. Cheng and C-M. Cheng, J. Appl. Phys. 84, 1284 (1999); Philos. Mag. Lett. 77, 39 (1998)]. A parametric study of Y/E and n was conducted using the finite element method to model material behavior. Regression analysis was used to correlate the H/E findings from the simulations to Y/E and n. With the a priori knowledge of E, this correlation was used to estimate Y and n.

The effects of the precursor pH and sintering temperature on the synthesizing behavior and morphology of mullite were studied using a stoichiometric mullite (3Al2O3 · 2SiO2) precursor sol. The mullite precursor sol was prepared by the dissolution of aluminum nitrate enneahydrate [Al(NO3)3 · 9H2O] into the mixture of silica sol. The precursor pH of the sols was controlled to the acidic (pH ≈ 1.5 to 2), intermediate (pH ≈ 4.5 to 5) and basic (pH ≈ 8.5 to 9) conditions. The gels dried from the synthesized aluminosilicate sols were formed into a disk shape under 20 MPa pressure; then the green bodies were sintered for 3 h in the temperature range of 1100–1600 °C. The synthesizing temperature of mullite phase was found to be above 1200 °C for pH ≈ 1.5 to 2, and above 1300 °C for pH ≈ 4.5 to 5 and pH ≈ 8.5 to 9. The grain morphology of the synthesized mullite was changed to a rod shape for pH ≈ 1.5 to 2, and granulate shape for pH ≈ 4.5 to 5 and pH ≈ 8.5 to 9 with increasing sintering temperature. It was found that the morphology of mullite particle was predominantly governed by precursor pH and sintering temperature. However, at higher pH, the precursor pH and sintering temperature did not affect the synthesis behavior and grain morphology.

Ba2MeWO6 (Me=Mg, Ni, Zn) double perovskites were prepared by the conventional solid-state reaction in a wide temperature range. Single-phase ceramics were obtained only at low temperatures approximately 1200°C, whereas a small amount of second phases existed in the samples sintered at higher temperatures. All the compounds are characterized by the cubic perovskite structure (space group Fm3m) with a complete NaCl type ordering between B-site ions. Anomalous temperature variation of the dielectric loss tangent found in the Ba2NiWO6 perovskite is supposed to be connected with a dielectric relaxation due to electronic hopping within thermally activated Ni3+-6W(6-1/6)+/W5+-6Ni(2+1/6)+ clusters. Dielectric measurements showed that the other two perovskites—Ba2ZnWO6 and Ba2MgWO6—exhibit a positive value of the temperature coefficient of permittivity. Such temperature variation is assumed to be caused by a considerable influence of the second polar mode involving B-site ion vibrations on the low-frequency dielectric properties.

The crystallographic structure and orientation of iron nanoparticles present in carbon nanotubes (CNTs) was studied when iron was used as a catalyst. It was found that while most of the nanoparticles encapsulated inside the CNTs had the expected α–Fe (body-centered-cubic) phase, a significant number of them formed and retained the γ–Fe (face-centered-cubic) phase that is not the normal bulk phase at room temperature (nor even expected to form at the growth temperature used). It was also found iron particles at the tips of the nanotubes were either α–Fe or cementite (Fe3C). On the basis of these observations and thermodynamics, a mechanism for the formation of these particles and insights into CNT growth is proposed.

Composite dielectric ceramics of BaTiO3/SrTiO3 were prepared using the spark plasma sintering (SPS) method. Relatively dense (>92% of the theoretical x-ray density) composite ceramics were obtained for a relatively short sintering time (∼3 min). Such a short sintering time was advantageous in suppressing the formation of a complete solid solution (Ba, Sr)TiO3. Fixed-frequency (100 kHz), room-temperature permittivity measurements of the BaTiO3/SrTiO3 = 9/1 composites showed a flat temperature dependence within the range 30–110 °C. X-ray diffractometry measurements showed that the current SPS-BaTiO3/SrTiO3 composites consisted of BaTiO3 and small amounts of (Ba1−xSrx)TiO3 with various x values having different phase transition temperatures. Such multicomponent microstructures would be responsible for the flat temperature dependence of permittivity.

Oxygen-containing precursor systems for the synthesis of mixed aluminum–gallium nitride (AlxGa1−xN with x = 0.1 to 0.5) through ammonolysis (heat treatment under ammonia) were evaluated. Three different precursor systems were studied: (i) aluminum isopropoxide (aluminum sec-butoxide)/gallium isopropoxide hydrolyzed with excess water and cross-linked with 1,6-hexanediol, (ii) aluminum–gallium hydroxide coprecipitated from aluminum–gallium nitrate solution, and (iii) spray-dried aluminum–gallium nitrate solutions. The specimens were heat-treated between 700 °C and 1100 °C and were characterized mainly by x-ray diffraction, nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). NMR was used to follow the conversion of oxygen to nitrogen bonds. TEM in combination with energy-dispersive x-ray spectroscopy was used to determine the solid-solution composition for separated particles. It is possible to synthesize a mixed hexagonal (Al,Ga)N with crystallite sizes in the range of ∼10 nm from all three precursor systems, but all products contained larger GaN crystals ranging from 20 nm (alkoxide-derived) to 200 nm (hydroxide-derived) and a fraction of untransformed Al–O bonds; e.g., (amorphous or γ-phase) Al2O3.

A series of coarse-grained BaTiO3 specimens with different dopant (Nb) concentrations were prepared by adjusting the oxygen partial pressure during sintering. They were again heat-treated in air, and the behavior of the grain boundary electrical properties with the increase of Nb concentration was investigated under the conditions of the same microstructure and heat treatment. The interface states of the grain boundaries were estimated using the grain boundary R (resistance) and C (capacitance) values at each temperature that were obtained from impedance analysis. An increase in the interface state density at certain energy levels with increasing Nb concentration was verified experimentally. One type of interface state was observed for specimens with low Nb concentrations and another for specimens with high Nb concentrations. It is proposed that the changes in the interface state with increasing Nb concentration are related to the transition of the compensating defect mode and differences in the extent of oxygen adsorption at the grain boundaries.

Composite Ba0.6Sr0.4TiO3/MgO thin films with 60% tuning and tan [H9254] of 0.007 at 2 GHz were deposited using metal organic decomposition inks by spin coating on single crystal MgO substrates. The films with approximately 1 mol% MgO in Ba0.6Sr0.4TiO3 had a better tuning/loss ratio than either the 0 or the 10 mol% MgO substituted films. Crystalline Ba0.5Sr0.5TiO3 films were produced on both MgO and alumina substrates by inkjet printing of metalorganic precursors with subsequent thermal decomposition followed by annealing at 900°C. Barium strontium titanate lines as narrow as 100 μm were printed on the alumina substrates. The inkjet-printed films were predominantly (100) oriented on MgO and (110) oriented on alumina. The crystalline quality of the inkjet-printed films was improved by annealing at 1100°C for 3 h in oxygen. Both the printed and the spin-coated films had smooth surfaces (300 Å root-mean-square roughness) as required for subsequent deposition of high-resolution metal electrodes. An inkjet-printed Ba0.5Sr0.5TiO3 film (3500 Å) on MgO annealed at 1100°C had 20% tunability of the dielectric constant (ε) at 9.1 V/μm direct current bias and tan δ < 0.002 at 1 MHz.

TlGa1−xSbxS2 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) single crystals were grown using the Bridgman–Stockbarger method. The direct energy gaps of the single crystals were found to be 2.586, 2.459, 2.344, 2.228, 2.119, and 1.987 eV for the composition x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, respectively, at 20 K. The indirect energy gaps were found to be 2.479, 2.357, 2.232, 2.118, 1.983, and 1.871 eV for the composition x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, respectively, at 20 K. The optical energy gaps decreased linearly with increasing composition x. The temperature dependence of the optical energy gaps for each of the single crystals was well fitted with the Varshni equation.

Lead zirconate titanate (PZT) films between 1 and 3 μm thick were grown using solution deposition techniques to study the effects of crystal structure and orientation on the direct piezoelectric output of these films on platinized Si membranes. By varying the chemistry of the film from Zr-rich to Ti-rich, the {100}/(111) relative intensity increased for films grown on randomly oriented Pt films. The 40:60 PZT had a tetragonal crystal structure and produced greater electrical output at a given strain than the rhombohedral film (Zr:Ti concentrations less than 50:50), while having a similar e31 constant, between 4.8 and 6.3 C/m2. Orientation and voltage output at a given strain were not strongly influenced by thickness in the ranges investigated. Defects in internal PZT/PZT crystallization interfaces were identified and include porosity on the order of tens of nm, with a corresponding depletion in Pb and accumulation of O at these interfaces. The {100} texture of rhombohedral films deposited upon (111) textured Pt films is significantly greater than the {100} texture of tetragonal films, which show both a {100} and {111} orientation on the same Pt film.

By the combination of two successive dry milling processes (i.e., by using a multiring mill and subsequently a pin-type disintegrator), downsizing of Si powders was achieved to 30 nm crystallites and their aggregated mean volume diameter about 100 nm, with the top size less than 400 nm. Combination of the two dry milling processes proved to be effective to reduce the particle size and sharpen the size distribution of the aggregates without using any additives, tedious wet processes, or subsequent classification. Increase in the impurity due to milling was <0.1% for Fe and <0.4% for Zr, being well within a tolerable limit for most of the technological purposes.

The method of electro-deoxidation was applied to reduce solid Nb2O5 directly to niobium metal, in the form of sponge, in the eutectic CaCl2–NaCl and BaCl2–NaCl systems, respectively. The direct electrochemical reduction of solid Nb2O5 was achieved by electrolysis in the chloride melts at temperatures between 850 and 950 °C and at a controlled potential of 3.1 V, well below the decomposition potentials of the melts used. The obtained results demonstrated that the method is applicable for preparing niobium sponges directly from solid Nb2O5 under the present experimental conditions. The niobium sponge prepared was proven to possess as remarkable superconducting properties. The parameters affecting the rate and the extent of electro-deoxidation were investigated experimentally, including initial particle sizes of the starting Nb2O5 powders, compaction pressure, sintering temperature and times, electrolysis temperature and duration, and electrolyte systems. The mechanism by which the Nb2O5 pellets were electro-deoxidized to the niobium sponges was also discussed on the basis of the present experimental observations.

A pseudoternary alloy system was constructed by combining icosahedral quasicrystal (IQC), decagonal quasicrystal (DQC), and Zr into one alloy system. Different proportions of Zr were added into pseudobinary alloy IQC80DQC20 (in wt.%). The structural evolution in these alloys is discussed. An amorphous alloy composition was found in this system. Melt-spinning amorphous alloy was produced in this composition. Through differential scanning calorimetry experiments, the amorphous alloy exhibited a high glass-forming ability comparable to that of the Inoue alloy Zr65Al7.5Cu17.5Ni10.

Several procedures have previously been advanced for extracting constitutive relations from the force–displacement curves obtained from indentation. This work addresses the specific problem of determining the elastic modulus E, yield stress Y, and hardening exponent n, which define the isotropic strain-hardening model from a single force–displacement curve with a sharp conical tip. The sensitivity of the inversion process was tested through a series of finite element calculations using ABAQUS. Different magnitudes of normally distributed noise were superimposed on a calculated force–displacement curve to simulate hypothetical data sets for specific values of E, Y, and n. The sensitivity of the parameter confidence intervals to noise was determined using the χ2-curvature matrix, statistical Monte Carlo simulations, and a conjugate gradient algorithm that explicitly searches the global parameter space. All three approaches demonstrate that 1% noise levels preclude the accurate determination of the strain-hardening parameters based on a single force–displacement curve.

Finite-element analyses for elastoplastic cone indentations were conducted in which the effect of linear strain hardening on indentation behavior was intensively examined in relation to the influences of the frictional coefficient (μ) at the indenter/material contact interface and of the inclined face angle (β) of the cone indenter. A novel procedure of “graphical superposition” was proposed to determine the representative yield stress YR. It was confirmed that the concept of YR applied to elastic-perfectlyplastic solids is sufficient enough for describing the indentation behavior of strainhardening elastoplastic solids. The representative plastic strain of εR (plastic) ≈ 0.22 tan β, at which YR is prescribed, is applicable to the strain-hardening elastoplastic solids, affording a quantitative relationship of YR = Y + ε;R (plastic) × EP in terms of the strain-hardening modulus EP. The true hardness H as a measure for plasticity is estimated from the Meyer hardness HM and then successfully related to the yield stress Y as H = C(β,μ) × Y for elastic-perfectly-plastic solids and as H = C(β,μ) × YR for strain-hardening solids, by the use of a β- and μ-dependent constraint factor C(β,μ) ranging from 2.6 to 3.2.

Control over crystallographic orientation in thin films is important, particularly with highly anisotropic structures. Because of its ferroelectric nature, the layered perovskite La2Ti2O7 has interesting piezoelectric and electrooptic properties that may be exploited when films are highly textured. Sol-gel films with an orientation factor of greater than 95% were fabricated without relying on epitaxial (lattice-matching) growth from the substrate. Film orientation and crystallization were confirmed by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and optical measurements. The particle sizes in all precursor solutions were measured by dynamic light scattering experiments. Experimental results indicate that film orientation is a function of precursor solution concentration, size of the molecular clusters in the solution, and film thickness.

Liquid-phase sintered SiC, doped with 3 vol% AlN, Al2OC, Y3Al5O12, revealed a variation in electrical resistivity of more than five orders of magnitude (<102-107 Ω cm) upon slight variations in the sintering process. The materials were characterized using various transmission electron microscopy techniques such as high-resolution transmission electron microscopy (HRTEM), Fresnel fringe imaging, analytical electron microscopy, and electron holography. The main focus of this study was to verify whether there is a correlation between interface structure and electrical resistivity. Scanning electron microscopy (SEM) of polished and plasma-etched surfaces showed interface features similar to those observed in Si3N4 ceramics containing amorphous grain-boundary films. Such films are expected to act as an insulating barrier for electric current. However, in contrast to the SEM results, HRTEM of SiC grain boundaries revealed no intergranular film in any of the SiC materials studied. Elemental analysis (i.e., energy dispersive x-ray and electron energy loss spectroscopy) of these “clean” SiC interfaces showed the segregation of secondary phase elements at grain boundaries. Electron holography and the Fresnel fringe technique were used to determine the change in the mean inner potential across SiC interfaces, which could be associated with the spatial charge distribution of a double Schottky barrier. The height of the potential barrier correlates with the electrical resistivity recorded via impedance spectroscopy.

The change in microstructure associated with the decrease in critical current density (Jc) of Yba2Cu3O7−δ (YBCO) films with increasing thickness was examined. Samples of pulse laser deposited YBCO films varying in thickness from 0.19 to 3.0 μm on rolling-assisted biaxially textured substrates with an architecture of CeO2/YSZ/CeO2/Ni were prepared by tripod polishing for cross-sectional electron microscopy. More randomly oriented grains in the upper portion of the YBCO film surface were observed with increasing film thickness, resulting in less cube texture. In addition, increases in mismatch across the boundaries of the c-axis grains with increasing time during deposition, along with the development of BaCeO3 and Y2BaCuO5 phases at the YBCO/CeO2 interface, contributed to the degradation of film properties. Surface outgrowths of the YBCO film were examined as well as the defect structures and second-phase formations within the films.