Effects of Valence States of Additions on the Grain Growth and Electrical Properties of Low Breakdown Voltage ZnO Varistors

Grain growth and electrical properties in ZnO system with various valence states of manganese and cobalt were studied. The results were discllssed by means of defects produced by the additions. The grain growth was analyzed from the kinetic grian growth equation: Gn =Dtexp(-E/RT). The results show that the grain growth kinetic exponent n is 6 and activation energy is 224±17kJ/mol. The grain size increases with the valence states of manganese and cobalt.Raising the firing temperatures can decrease the breakdown voltage, but the leakage current will increase and its nonlinear coefficient will decline when the firing temperature is too high. In general,the firing temperature is ndt exceed 1250℃.