Microstructural Effects on Electrical Behaviour of ZnO-Based Varistors

Abstract. The zinc oxide (ZnO) based varistor is a multicomponent oxide ceramic material. The electrical behaviour of the varistor depends on the microstructure of the ceramic mixture which is composed of primarily ZnO and other metal oxide constituents such as Bi2O3, Sb2O3, CoO, MnO, and etc. The microstructure controls mainly the varistor parameters such as breakdown voltage and coefficient of non-linearity. This work explains relations between the microstructures and electrical behaviours in differently processed ZnO-based varistor systems. For this purpose, optical and scanning electron microscopy were conducted to characterize the microstructural features of the varistor pellets. The grain sizes and size distributions were measured using image analysis. A dc power source was used to measure the electrical properties.