Zinc oxide varistors are semiconductor ceramics, which their excellent nonlinear electrical characteristics which are induced from their grain boundaries and depend on their microstructures. Based on a theoretical aspect, finer primary particles with a narrow size distributions offer better electrical properties. Then these properties are related to the size and morphology of ZnO grains. In this research, zinc oxide micro and nano powders were synthesized by a sol-gel method and the effect of the ZnO particle size on the electrical properties of zinc oxide varistors was investigated. The results showed that if ZnO nano powder is used instead of micro powder for fabrication of varistors, the sintering time and temperature were decreased; also, the electrical properties such as the nonlinear coefficient and breakdown voltage were increased up to 43 and 4750 V/cm versus 34.8 and 2920 V/cm respectively.

Keywords: Varistor, ZnO, Electrical property, Nano powder, Nonlinear coefficient, Break down voltage.