Zhang Zhongtai

Temperauture-humidity-gas multifunctional sensitive ceramics

Abstract A new multifunctional sensitive ceramic, BaTiO 3 BaSnO 3 (BTS), which is a p-type metal-oxide porous ceramic semiconductor, has been studied. It is capable of detecting temperature, humidity and gas type with a single sensing element. This paper presents results of research on multifunctional sensitive ceramics. The crystalline phase, porous structure, semiconducting properties and the relationships between the sensitive characteristics and the meso-macrostructure of the pores of BTS porous ceramics have been investigated.

Acceptor compensation in (Sb,Y)-doped semiconducting Ba1−xSrxTiO3

The characteristics of semiconducting Ba1-xSrxTiO3 samples with different doping procedures were studied. Complex impedance-measurements were used to separate the resistances of grains Rb, and grain boundaries as Rgb. It was shown that excess donors added after calcination diffused into the grain bulk more slowly and could be compensted on the grain boundary by acceptors, and thus samples with particularly low resistivity were obtained. Using an excess donor to compensate for the acceptor, a sample with room temperature resistivity of ∼200 Ω cm-1 and greater than 7.8 orders of jumping of resistance was obtained.

Sol-Gel Derived Cubic-Phase WO3 Nanowires on Nano- Porous Alumina Template

WO3 nanowires with various morphologies were prepared on nanoporous alumina template by a simple sol-gel method. X-ray diffraction analysis reveals that the obtained materials are cubic WO3. Scanning electron microscopy shows that the products contain chrysanthemum-shaped WO3 nanowires. The diameter of WO3 nanowires is about 10-80 nm and their length is up to several micrometers. Argon gas atmosphere is more favorable for WCl6-triblock copolymer sol to form WO3 nanowires with different morphologies on nanoporous alumina template than air atmosphere.

Citric Gel Synthesis and Luminescent Properties of Ce3+-Activated SrGa2O4 Phosphor

Ce3+ -activated SrGa2O4 phosphor was synthesized by a method of citric gel, wherein citric acid served as a chelate agent, and the as-synthesized powder was calcined in a slightly reduced ambient. The crystallization characteristics of the sample varied with the calcining temperature. Compared with the phosphor prepared by the solid-state reaction, the phosphor synthesized by citric gel was calcined at a relatively lower temperature. Consequently, the volatilization of Ga2O3 during high-temperature calcining process was avoided. The typical double-peak emission of Ce3+ originated from 2D(5d)→4F5/2(4f), and 2D(5d)→4F7/2(4f) was observed, and the intrinsic emission of SrGa2O4 host was much restricted. The emission intensity varied with the calcining temperature because the different crystallinity and the optimal concentration of Ce-dopant was determined at 3%.

Synthesis and performance of carbon-modified LiFePO4 using an in situ PVA pyrolysis procedure

LiFePO4/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 atmosphere with polyvinyl alcohol (PVA) as the carbon source. The influences of carbon content on the microstructure and battery performance were investigated. Single LiFePO4 phase and amorphous carbon can be found in the products. A special micro-morphology of the optimum sample was observed. The discharge capacity of the cell with the optimum cathode was 135 mAh.g−1, close to the charge capacity of 153 mAh.g−1 at 17 mA.g−1. The influence of ambient temperature on the cell capacity was investigated. The temperature dependence of its electrochemical characteristic was evaluated by using AC impedance spectroscopy. A new equivalent circuit based on the charge and mass transfer control process in an electrode was proposed to fit the obtained AC impedance spectra. The tendency of every element in the equivalent circuit was used to interpret the temperature dependence of the capacity of the optimum cathode.