Characteristics of Zinc Oxide Varistor Ceramics sintered at high temperature

Abstract

The microstructural and electrical characteristics of ZnO based varistors, which are composed of ZnO-Bi 2 O 3 -MnO 2 -Cr 2 O 3 -Sb 2 O 3 and Co 3 O 4 are studied in relation to sintering temperature, in the range of 1200° C 1250° C. Microstructure, and electrical properties were studied by scanning electron microscopy (SEM) and direct current electrical measurement. The varistor ceramics had fine microstructures, the grain size varied from 2.23 to 2.96 $\mu \mathrm { m }$. In the examined temperature range, the breakdown field decreased from 2889.76 to 2189.76 V/cm with the increase of sintering temperature, and the nonlinear coefficient $\alpha$ decrease from 31.21 to 25.13. The optimal samples obtained from the varistor sintered at 1200° C have average grain size of about 2.23$\mu \mathbf { m }$, breakdown field 2889.76 V/cm, the average breakdown voltage per grain boundaries $\mathbf { V } _ { g b }$ of 0.64 V, the leakage current $\mathbf { J } _ { L } = 0.20 m A / c m ^ { 2 }$ and the nonlinear coefficient of 31.21.