The Research On SrTiO₃-Based Varistor Materials

SrTiO3-based varistor is a kind of new multifunctional semiconductor ceramics materials developed since 1980s, which is being widely used in all kinds of low-voltage fields, such as in large-scale integrated circuit and semiconductor electronic applications. The research is carried out aimed at the preparation of SrTiO3-based varistor ceramics and the dependence of acceptor dopants and heat-treatment process on the electrical properties. The thesis contributes the following contents:The optimum experimental scheme has been achieved through the analysis of primary experimental results and the following sixteen group experimental results. Furthermore, SrTiO3-based varistor ceramics materials with excellent electrical properties were prepared, and various electrical properties are as follows: varistor voltage V1mA=(8.1-28.4)V·mm-1;nonlinear coefficient α=2.5-8.8; relative dielectric constant εr=(1.67-6.70)×105; dielectric loss tanδ=(4.77-23.23)%。The effects of Li and Mn doping on the electrical properties of SrTiO3-based varistor ceramics were investigated. The results show the varistor ceramics can obtain ideal electrical properties doped with Li and Mn together. However, when Li and Mn were properly doped together, the samples acquired excellent electrical properties: V1mA=(5.7-11.7)V·mm-1; α=6.8-11.0; εr=(2.4-4.4)×105; tanδ=(7.1-10.4)%. When the contents of Li2CO3 and MnCO3 were 1.00mol% and 0.05mol% respectively, the nonlinear coefficient α reached the largest value of 11.0. Compared with Mn doped only, the addition of Li increased the α value significantly. The influences of oxidizing heat-treatment process on the electrical properties of SrTiO3-based varistor ceramics were investigated. The results indicate that both the oxidizing heat-treatment temperature and time play an important role in determining the varistor characteristics and dielectric properties. With increasing the time and temperature of oxidizing heat-treatment, the varistor voltage and nonlinear coefficient increase, while the relative dielectric constant and dielectric loss decrease. Finally, the characteristics of grain boundary electron barrier were described properly with superimposed barrier model.