We conducted hydrostatic compression and constant-stress-difference experiments, with and without an applied electric field, on poled, niobium-doped lead zirconate titanate ceramic. The objective was to quantify the effects of nonhydrostatic stress and electric field bias on electromechanical behavior of the ceramic during the ferroelectric, rhombohedral → antiferroelectric, orthorhombic phase transformation. Increasing stress difference (shear stress) decreases the mean stress at which the transformation occurs. Increasing shear stress also retards the rate of transformation, causing reductions in both the rate of charge release and peak voltage attained during depoling. Application of the electric field bias slightly increases the transformation pressure for poled ceramic. Previously, we showed that under nonhydrostatic stress, the transformation took place in unpoled ceramic when the maximum compressive stress equalled the hydrostatic pressure at which the transformation would otherwise occur. This simple stress criterion does not apply to poled ceramic. However, poled material has a preferred crystallographic orientation and mechanical anisotropy, whereas unpoled ceramic is isotropic. We present a qualitative model for the transformation under nonhydrostatic stress-related to that anisotropy, which resolves these seemingly disparate observations.

Stoichiometric CaAl2Si2O8 gels prepared by the Pechini process crystallize to triclinic anorthite via an intermediate, previously unknown pseudohexagonal phase. Hydrothermal treatment of this pseudohexagonal phase at 350 °C transforms it to hexagonal anorthite. These combined processes produce the hexagonal phase via a low-temperature, chemical route in contrast to the conventional high-temperature melting and crystallization method. Powder x-ray diffraction data and nuclear magnetic resonance (NMR) spectra of the hexagonal anorthite agree well with the published structure. They indicate a high degree of tetrahedral Si/Al ordering within the layers, but long-range disorder in the average structure due to (001) stacking faults present between the layers.

The formation of metastable tetragonal zirconia nanophase by thermal treatment of a zirconia gel derived from zirconyl chloride has been studied by high-resolution transmission electron microscopy (HRTEM) and differential scanning calorimetry (DSC). HRTEM observations revealed that a fully crystallized sample consists of nanocrystals, around 13 nm in size. This nanocrystalline t-ZrO2 has practically the same crystal structure as that of the high-temperature tetragonal zirconia phase. The nonisothermal crystallization rate is very fast in as-prepared zirconia gel. DSC data at various heating rates can be described by a two-parameter model which predicts the crystallization kinetics in isothermal conditions very well. The Johnson–Mehl–Avrami (JMA) model can be used, however, in partially crystalline samples (crystallinity >30%) where the rate of crystallization process is considerably slower. The kinetic exponent of the JMA model (m = 1.0 ± 0.1) then corresponds to linear dependence of the crystallization rate as a function of the fraction crystallized.

The synthesis of barium titanate (BaTiO3) was investigated in water at 90 °C in the presence of polymeric additives. Homopolymers (polyacrylic acid) and block copolymers (polyethylene oxide-block-polymethacrylic acid) were added during synthesis to influence particle morphology and size distribution. The polymers affected the morphological evolution of the forming powder by adsorbing preferentially on specific planes. The polymeric species additionally slowed the formation of barium titanate. The barium concentration also changed the morphology, particle size, and other powder characteristics.

Films of nominal composition Pb(Zr0.53Ti0.47)O3 (PZT) in the thickness range 0.25−10 μm have been fabricated on Pt/Ti/SiO2/Si substrates using a propanediol-based sol-gel route. The spun-on coatings were prefired at 350 and 600 °C between successive depositions before firing the multilayer stack at 700 °C for 15 min. The variations in crystallite orientation, microstructure, and dielectric and ferroelectric properties were determined as a function of film thickness. For a constant applied field of 150 kV cm−1, remanent polarization decreased progressively from 35 to 17 μC cm−2 as film thickness decreased in the range 10–0.25 μm; values of coercive field were reasonably constant, 18–19 kV cm−1, for films between 2 and 10 μm, but increased sharply below 2 μm, reaching 46 kV cm−1 for a 0.25 μm film. Relative permittivity (εr) decreased from approximately 1400 to approximately 940 with most of the reduction occurring in films less than 2 μm in thickness. These trends are discussed in terms of the presumed influence of interfacial phenomena on the measured electrical response.

We report on the properties of BaBi2Ta2O9 (BBT) thin films for dynamic random-access memory (DRAM) and integrated capacitor applications. Crystalline BBT thin films were successfully fabricated by the chemical solution deposition technique on Pt-coated Si substrates at a low annealing temperature of 650 °C. The films were characterized in terms of structural, dielectric, and insulating properties. The electrical measurements were conducted on Pt/BBT/Pt capacitors. The typical measured small signal dielectric constant and dissipation factor, at 100 kHz, were 282 and 0.023, respectively, for films annealed at 700 °C for 60 min. The leakage current density of the films was lower than 10−9 A/cm2 at an applied electric field of 300 kV/cm. A large storage density of 38.4 fC/μm2 was obtained at an applied electric field of 200 kV/cm. The high dielectric constant, low dielectric loss and low leakage current density suggest the suitability of BBT thin films as dielectric layer for DRAM and integrated capacitor applications.

The microstructure and the defects of ZnO coatings deposited at room temperature by sputtering onto fibers and flat substrates were characterized using transmission electron microscopy (TEM), scanning electron microscopy, and x-ray diffraction (XRD). XRD shows that the films have a [0001] preferred orientation and a large angular width of the 0002 reflection. According to TEM observations, the film microstructure consists of columnar grains which contain large concentrations of basal planar defects and dislocations. High-resolution transmission electron microscopy analysis and the associated image simulation are in full agreement with the presence of single (type I) and double (type II) stacking faults. The relation between the observed defects and the 0002 peak broadening is discussed.

A polymeric precursor for the Si3N4–SiC–Y2O3 ceramic system was synthesized by block copolymerization of perhydropolysilazane (PHPS) with hydroxy-polycarbosilane (PCS-OH), followed by chemical modification with yttrium methoxide. Fully dense Si3N4–SiC–Y2O3 ceramics were successfully synthesized by pyrolysis of the polymeric precursor at 1000 °C, followed by hot pressing at 1800 °C in N2. The resulting ceramics revealed that β–SiC particles were dispersed in a size range of about 10–600 nm, and a large amount of β–SiC submicron particles were segregated at the β–Si3N4 matrix grain boundaries. It was found that the yttrium-modified block copolymer of PHPS and PCS-OH yielded unique binary ceramics composed of β–SiC–Y2O3 and β–SiC nanoparticle-dispersed Si3N4–Y2O3.

This paper discusses the induction of residual stresses during the curing process of thin titania layers, which are derived using a sol-gel process. During this process, stresses may build up in the spinning stage, the drying stage, and the consolidation stage. The magnitude and character of these stresses depend heavily on the morphology of the layers in the various stages and the processing conditions. Dried layers are densified using two different processes, conventional furnace heating and laser heating. X-ray analysis and scanning electron microscopy are used as tools to study crystallization, grain growth, phase transformation, and the evolution of residual stress fields in the thin titania layers. Through an extensive study of the residual stress state in the layers, more insight is gained in the evolution of stresses during the curing process of sol-gel-derived thin titania layers.

Microstructural evolution and mechanical properties of gas-pressure-sintered Si3N4 with 4 wt% Yb2O3 as a sintering aid were investigated. The microstructure was not uniform throughout the specimen. Extremely large elongated grains were formed at the outer region near the surface, while relatively small elongated grains were formed at the inner region of the specimen. The outer region expanded inward with the sintering time. Mechanical properties, such as flexural strength, fracture toughness, and R-curve behavior of the specimens were strongly influenced by these variations in microstructure. The fracture toughness and the R-curve behavior of the outer region were higher than those of the inner region of the same specimen. On the other hand, the strength of the inner region was higher than that of the outer region. By controlling the relative thickness of each region, Si3N4 specimens having functionally graded microstructure were obtained. The Si3N4 with such microstructure exhibited high strength, high fracture toughness, and good flaw tolerance at the same time.

Several experiments have been conducted to assess the possible mechanisms for the inhibition of reduction of Ca2+-doped barium titanate in a reducing atmosphere. Three methods, i.e., conventional, semiwet, and citrate processes, have been used to prepare the powders. It was found that the formation mechanism would influence the occupation of Ca2+ in the B site. Moreover, it was concluded that Ca2+ occupation of the B site is the major cause for the inhibition of reduction of Ca2+-doped barium titanate. Ti deficiency would be the driving force for Ca2+ to occupy the B site.

Nickel hydroxide powders currently used in the positive electrode of nickel-metal hydride (Ni–MH) batteries require cobalt or cobalt oxides to make them viable and attractive. As a step to eliminate the cobalt-containing materials, spherical nickel hydroxide powders coprecipitated with Zn(OH)2 were prepared by a spraying technique. These powders, which have a higher tapping density and a much smaller pore volume than conventional powders, were used as the active materials of nickel hydroxide electrodes. The effects of the Zn(OH)2 additions on the electrode properties, such as percentage utilization and cycle life, were studied, and the relationship between the electrode performance and the formation of γ–NiOOH was investigated. The cycle life was increased because there was less electrode swelling due to much reduced formation of γ–NiOOH.

Nanosized Ce-doped silica particles (without and with Al addition) dispersed within pores of mesoporous silica host were synthesized by soaking and sol-gel technique. It was found that the dispersed phosphor particles are mainly located within the pores that are less than 4 nm in diameter. There exist two luminescence peaks at about 350 and 700 nm, respectively, for this phosphor in the dispersed or aggregated state. For the dispersed system, the luminescence intensities of both peaks are more than 14 times higher than those of the aggregated one, the shoulders on the lower sides of the luminescence peaks disappear, and no effect of Al addition on the luminescence occurs which is in contrast to the aggregated system. This is mainly attributed to the high dispersity of nanosized phosphor particles in the host and the effective avoidance of a clustering of Ce3+ ions.

A new self-propagating high-temperature synthesis (SHS) process has been developed for synthesis of AlN powder under low nitrogen pressures. Al and NH4X (X = F, Cl, Br, or I) powders were mixed and pressed into a compact, which was placed in a reaction chamber filled with nitrogen. The combustion synthesis reaction was ignited by heating directly the compact, and high product yields (∼90%) were obtained under nitrogen pressures of around 0.5 MPa. The product yield was affected by the reactant composition, the nitrogen pressure, and the compact-forming pressure. The powder as synthesized consists mainly of fibers, coarse granules, and agglomerated fine particles, which become mostly smaller than 10 μm after grinding. A reaction process was also proposed that explains the effects of the experimental parameters on the product yield.

Ammonia-monochloroborane, NH3BH2Cl, has been synthesized from the reaction of ammonia-borane with HCl in Et2O. Decomposition of the solid under NH3 to 600 °C produced amorphous BN in 97% yield. The 11B magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of the amorphous BN is indicative of boron in the same environment as in hexagonal BN. Subsequent pyrolysis of the amorphous BN to 1000 °C produced turbostratic BN. Pyrolysis of NH3BH2Cl under vacuum to 1100 °C led to the formation of turbostratic BN as confirmed by x-ray diffraction (XRD) analysis. Gas evolution during this pyrolysis confirmed that the precursor loses H2 and HCl.

Rapid thermal processing of BaTiO3 and TiO2 pressed powders at 500 °C/min to 1250 °C for 2 h in an infrared furnace resulted in a mixture of Ba2Ti9O20, BaTi4O9, and TiO2. Further heat treatment at 1390 °C led to 96 vol% phase-pure Ba2Ti9O20 from an initial mixture devoid of any dopant. Heat treatment at rates decreasing to 5 °C/min facilitated agglomeration of TiO2. This, in turn, increased the diffusion distance required for reaction of BaTi4O9 and TiO2 to form Ba2Ti9O20.

The mechanism for combustion synthesis (CS) of AlN was investigated in the present paper. A novel quenching technique was developed to retain the high-temperature structure formed in the sample during the combustion process. Based on the microstructural observation of the quenched specimen and thermodynamic analysis, a two-step reaction mechanism for CS AlN, i.e., vaporization of Al and subsequent reaction with N2, is proposed.

The role of the electrical conductivity of the product and of the thermal conductivities of the reactants on self-propagating combustion synthesis was investigated through modeling studies. Similar studies were made to investigate the role of the relative density of the reactants. The effect of an imposed electric field on the results of the modeling analysis was considered. For any given imposed field, the wave velocity exhibited a maximum at a given normalized thermal conductivity, electrical conductivity, and relative density. The results are discussed in terms of the Joule heat contribution of the field and are compared with experimental observations.

High-temperature oxidative drop solution calorimetry was used to measure the enthalpy of formation of α− and β−Si3N4. Two different solvents, molten alkali borate (48 wt% LiBO2 · 52 wt% NaBO2) at 1043 and 1073 K and potassium vanadate (K2O · 3V2O5) at 973 K, were used, giving the same results. Pure α− and β−Si3N4 polymorphs have the same molar enthalpy of formation at 298 K of −850.9 ± 22.4 and −852.0 ± 8.7 kJ/mol, respectively. The unit cell dimensions of impure α−Si3N4 samples depend linearly on the O and C impurity contents, and so does the molar enthalpy of formation. The energetic stability of the α−Si3N4phase decreases when the sample contains O and C impurities. The experimental evidence strongly suggests that the impurities dissolve into the α−Si3N4 structure to form a (limited) isostructural solid solution series but that this solid solution series is energetically less stable than a mechanical mixture of pure (α or β) Si3N4, SiO2, and SiC. Thus, the α-phase is not stabilized by impurities and is probably always metastable.

Pure and deuterated titanium thin films 140 nm thick were deposited on 〈100〉 Si wafers by electron beam evaporation, keeping the substrate temperature at 150, 300, and 450 °C. Pure Ti samples were deposited in a high-vacuum condition, while for deuterated samples, deuterium high-purity gas was introduced in the deposition chamber during the process. Film composition was studied by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA), whereas structural characterization of the deposited layers was carried out by x-ray diffraction (XRD) using both the traditional Bragg–Brentano geometry and a parallel beam setup for pole figure measurements. Titanium films deposited in a high vacuum showed the hexagonal Ti structure (α−Ti) and grew with a double orientation at each of the examined substrate temperatures. Deuterated titanium films deposited at 150 °C had a compositional ratio Ti: D = 1: 0.35 and grew with a [111] oriented fcc structure, suggesting the formation at low temperature of a substoichiometric δ hydride phase. Deuterated films deposited at higher substrate temperatures revealed a lower deuterium content and XRD reflections corresponding to the hexagonal Ti phase. The present results were interpreted according to a temperaturedependent D2 adsorption mechanism at the surface of the continuously growing Ti film.