Yin-Lai Chai

The structure and properties of zinc titanate doped with strontium

Abstract Doped and undoped zinc titanate powders were prepared by a conventional solid state reaction technique using metal oxides. The characteristics of zinc titanate samples were found to depend on the heating conditions and the amounts of additions. It is shown that they are semiconductors, and the formation of SrTiO3, α-Zn2TiO4, rutile phase, morphology roughness and open porosity increase with increasing the amounts of doped Sr. The electrical resistivities of doped and undoped zinc titanate reveal a transition from semiconductor behavior to metal-like behavior as the temperature increased. All samples represent the V-type resistivity–temperature characteristic and possess the typical PTCR characteristics above room temperature.

Structure and dielectric relaxation properties of Na1−xLaxNb1−xCrxO3 perovskites

Na1−xLaxNb1−xCrxO3 perovskites were prepared by conventional solid-state reaction with x=0.01, 0.05, 0.1, 0.2, 0.3, and 0.4. The structure with x=0.01 is similar to that of NaNbO3 with an orthorhombic structure. The crystal structure for compositions for x over 0.05 was found to have a distorted cubic structure. Grains of microcube topography were obtained. The average grain size is about 1–2μm. The dielectric constants and dissipation factors were measured as functions of frequency (20Hz–1MHz) and temperature (225–500K). The activation energy for x=0.2, 0.3, and 0.4 were 0.22, 0.21, and 0.19eV, respectively. Space charge polarization and orientational polarization contribute to the observed dielectric behavior.

Residual stress and thermal stability of the Fe-Ni-Cr/Invar bimetal membrane used for microactuation

Abstract The residual stress and Youngs modulus of Fe–Ni–Cr (FNC)/Invar bimorph, FNC, and Invar single-layered polycrystalline thin films were evaluated by the load–deflection method. It is found that the residual stress, microstructure, and sheet resistance are clearly correlated. The thin film stresses, determined by the bulge test, depend strongly on the working pressure and change from highly compressive to highly tensile in a narrow pressure range. The residual stress of both bilayers and single-layers can reduce to a relatively low level and can be stabilized with an annealing treatment. Thus, a bimorph wrinkle (or buckle) free membrane with low residual stress level and stable mechanical properties can be fabricated. These fabricated units may be used for microactuation devices.

Structure and dielectric properties of lower valence compensation for Ba1-xNax(FeTa)0.5O3 by reaction sintering process

ABSTRACT Complex perovskite oxides of Ba1-xNax(FeTa)0.5O3 (BNFT, x = 2, 4, 6, 8, 14, and 20 mole%) dielectric ceramics doped with lower valence compensation ions were prepared by a reaction-sintering process. The BNFT dielectrics were sintered at 1300°C for 8 h without calcinations involved. Due to low melting point of Na2CO3, the sintering temperature of dielectric decreased. The density of sintered dielectrics increased with increasing Na+ ion concentration and it cause BNFT dielectric surface glossy. The relative densities of sintered dielectrics were higher than 89.5%. The dielectric constant of Ba0.96Na0.04(FeTa)0.5O3 1300°C sintered ceramic was about 9 × 105, measured at room temperature at frequency of 1 kHz. The temperature-dependent loss curves measured in temperature range of −15∼90°C and frequency of 1 k∼1 MHz indicated that the samples exhibit a typical relaxor behavior with a broad temperature range which was contributed by orientation and space charge polarization.