Effect of sintering process on the electrical properties and microstructure of Ca-doped ZnO varistor ceramics

Abstract

The electrical properties of Ca-doped ZnO varistor ceramics are affected by sintering temperature. The samples exhibit excellent electrical properties and microstructure at a sintering temperature of 1050 °C. The ZnO varistor ceramics sintered at 950 °C have the best voltage gradient value, but their nonlinearity and leakage current are very poor. At different sintering temperatures, the grain boundary behavior of ZnO varistor ceramics is different. The grain boundary barrier increases with the increase in the surface state concentration, and it reaches the optimal value at the sintering temperature of 1050 °C. The electrical properties of the samples at the sintering temperature of 1050 °C are as follows: breakdown voltage E1mA = 529 V/mm, leakage current JL = 0.13 μA/cm2, and nonlinearity coefficient α = 92.