Preparation And Performance Of The Dual-function Pressure-sensitive Ceramic Strontium Titanate

SrTiO₃-based voltage-sensitive ceramics is a kind of new multifunctional semiconductor ceramics materials developed since 1980s, it has low breakdown voltage, excellent nonlinear coefficient, high dielectric constant and low dielectric loss. They belong to capacitor-varistor multifunctional ceramics (MFC) and have characteristics of high frequency noise absorption, burst pulse absorption ,surge absorption and self-recovery. The research is carried out to focuse on the influence of donor and its morphology, acceptors, sintering process and heat-treatment process to the electrical properties and microstructure of SrTiO₃-based varistors, and use nano-dopant to improve the properties of it. Some correlated results have been attained.The result shows that the kind, morphology and concentration of donor ions and dopant concentration, the kinds of acceptor ions, sintering temperature and heat-treatment process have significant influence on the microstructure and electrical properties.Under the condition of (N₂+C) reducing atmosphere, the SrTiO₃-based double-functional ceramic doped CeO₂ or Y₂O₃ as single donor and doped MnCO₃ and CuO as acceptor respectively have superiority on lower breakdown voltage, high nonlinear coefficient and high dielectric constant. Comparatively, samples doped CuO as acceptor and 1.2mol% Y₂O₃ as single donor have better general electrical properties: V_1mA=5.51V, α =5.8, ε_r=9.64×10⁴, tan δ =0.35.SEM images of samples indicate that raising sintering temperature can promote the growth and homogenization of grain. The paper studies the influence of heat-treatments process on the electrical properties of SrTiO₃-based varistor. The results show that both the time and temperature of heat-treatment play an important role in the determining the voltage-sensitive characteristics and dielectric properties. With the increasing of the oxidizing heat-treatment time, the breakdown voltage and nonlinear coefficient increase; With the increasing of the oxidizing heat-treatments temperature, the nonlinear coefficient increases and the breakdown voltage increases first and then descends.Nano-donor La₂O₃ can improve the microstructure of this materials and get better electrical properties as donor, and can get the double function ceramics with lower breakdown voltage and higher nonlinear coefficient: V_1mA=4.35V, α =6.2.Finally, this paper has discussed the grain boundary barrier of SrTiO₃-based varistors preliminarily. And based on the superimposed potential barrier model of grain boundary of SrTiO₃, under the condition of simplification, this paper analyzes the effect of the acceptor-diffused layer on the boundary barrier, and gets some useful rules.