Effects of the Er2O3 doping on the microstructure and electrical properties of ZnO–Bi2O3 based varistor ceramics

Abstract In the present study, the effects of Er2O3 doping on the phase, microstructure, and electrical properties of ZnO–Bi2O3 based varistors were systematically investigated. In particular, a correlation between the microstructure and electrical properties was established based on the quantitative analyses of grain size, grain size distribution, and porosity. It was found that appropriate Er2O3 content of 0.4 mol% effectively decreased the grain size and improved the homogeneity of grain size distribution, contributing to a well-connected Bi2O3 intergranular network. Thus, simultaneously enhanced voltage gradient of 280 V/mm and relatively high nonlinear coefficient of 46 were achieved in varistors. However, with further increasing Er2O3 content, the excess Er2O3 phases were generated and agglomerated at grain boundaries. This further caused coarse pores and seriously undermined the connectivity of Bi2O3 networks, leading to the decrease in nonlinearity of varistors. Furthermore, such a correlation revealed in this study may provide valuable guidelines for developing high-performance ZnO–Bi2O3 based varistors.