The influences of annealing temperature on the microstructure and electric properties of ZnO varistors

In this paper, the microstructure, phase structure and electric properties of the ZnO varistors after annealing at different temperature were researched. The varistors were prepared by the ordinary sintering process using the raw powders crushed and mixed in a high-energy ball milling. From the results of SEM and XRD, it was found that the thickness of the grain boundary was broadened with the increase of temperature. This phenomenon was raised by the phase transition of Bi₂O₃ in the phase boundary. To make clear the influence of the annealing temperature on the I-V nonlinear property of the varistors, the donor density, acceptor density, barrier height and activation energy of the varistors subjected to the different annealing temperature ranging from 673 K to 973 K were also studied by capacitance-voltage test and impedance test.