Electrical properties of ZnO varistors prepared by microwave and conventional sintering process

Abstract

The Bi₂O₃-based ZnO varistor materials were prepared by 2.45 GHz microwave, 24 GHz millimeter-wave or conventional-sintering processes. Both millimeter-wave and microwave sintering processes are superior to the conventional sintering process in densifying the Bi₂O₃-based ZnO materials. Large nonlinear coefficient and low leakage current density were attained by sintering the samples under the 1200°C sintering temperature and 5 min soaking time, A high density as 96.7% T.D. (theoretical density) has been achieved. However, the varistor characteristics, including breakdown voltage (V_bk), nonlinear coefficient (α) and leakage current density (J_L), degraded markedly for the samples sintered at too long soaking time (10 min), which was ascribed to the occurrence of abnormal grain growth, in accompany with the loss of Bi₂O₃ and ZnO species.

Keywords:

• ZnO varistor; microwave sintering