Microstructure of ZnO-glass varistors

The microstructure and compositions of ZnO-glass varistors prepared by sintering were analyzed by means of SEM, TEM, EPMA etc. Results show that ZnO-glass varistors consist of ZnO grains phase, Zn7Sb2O12 spinel phase and intergranular phase. A large amount of cobalt ions is dissolved in ZnO grains, while a small amount of manganese ions is dissolved in the surface layer of ZnO grains, and antimony ions is mainly located in the intergranular spaces. The thickness of grain boundary layer is about 10-100 nm, and the composition of grain boundary is almost the same as that of grains. It is found that a Zn-B crystalline phase is formed in the intergranular phase when sintering temperature is high enough. The formation of this phase is favorable to enhance the nonlinear properties of ZnO-glass varistors.