Role of oxygen at the grain boundary of metal oxide varistors: A potentialbarrier formation mechanism

A model is proposed here to explain how the chemical features of metal oxid e varistors can alter their nonohmic physical behavior, based on nonohmic s imilarities in the electrical properties of ZnO- and SnO2-based varistors. The proposed model explains the electrical properties of ZnO- and SnO2-base d varistors before and after thermal treatments in oxygen- and nitrogen-ric h atmospheres, which cause similar changes in the nonohmic feature of these polycrystalline ceramics with greatly differing chemical compositions and microstructures. The model is based on the key role that oxygen plays in va ristor grain boundaries, independently of the type of ceramic system (ZnO-, SnO2- or even SrTiO3-based varistors) involved. (C) 2001 American Institut e of Physics.