Effects of sintering temperature on microstructure and varistor performances of ZnO-SrCO3-Co2O3 ceramics

Sintering temperature is decisive for optimizing the grain boundary environment to obtain the high performance ZnO based varistor ceramic. In this work, the impacts of sintering temperature on microstructure and electrical properties of ternary Zn-Sr-Co varistor were investigated. It was found that the distribution of Sr, the critical factor to form grain boundary, was heavily sensitive to sintering temperature. The considerable Sr ions precipitated at grain boundaries and formed the clusters of SrZnO2 while the sintering temperature increases from 1150 degrees C to 1190 degrees C. Besides, the precipitation of Sr led to the large segregation of Co at grain boundaries. The enrichment behavior of Sr and Co contributed to the optimization of grain boundaries, resulting in the enhanced barrier height. As a result, the excellent nonlinear current-voltage performances, i.e., the high nonlinear coefficient of 56.47 and the low leakage current density of 0.73 mu A/cm2 were obtained in the ternary ZnO-SrCO3-Co2O3 varistor sintered at 1190 degrees C. However, the grain boundary environment would be destroyed by the excessive temperature of 1210 degrees C, resulting in the degradation of grain boundary barrier and especially a surge in the leakage current IL from 0.73 to 92.19 mu A/cm2. In addition, varying sintering temperature has the important effects on impedance and dielectric properties of the ZnO-SrCO3-Co2O3 varistors. The findings provide new perspectives for developing the high-performance ternary ZnO-SrCO3-Co2O3 varistor ceramics by optimizing the initial grain boundary environment at different sintering temperatures.