Properties of ZnO varistors prepared with nano-sized powders

ZnO varistors with higher voltage gradients are expected in the power system, and the key to this property is to diminish the grain size. In this paper, nano-sized ZnO particles are used as the raw material in order to obtain small grains. Pellets are fabricated by two sintering methods: the conventional pressureless sintering and the spark plasma sintering (SPS). For the samples fabricated by the conventional sintering, the average grain size varies from 1 mu m to more than 10 mu m when the sintering temperature changes from 900 degrees C to 1200 degrees C. The voltage gradient can reach as high as 2020 V/mm. The grain size of the SPS samples is less than 1 mu m, and the voltage gradients can reach 963 V/mm.