We fabricated ZnO-Bi2O3-Sb2O3-Al2O3-CoO-NiO varistor and investigated the effect of sintering temperature on its microstructures and electrical properties. As the sintering temperature increases, crystalline grain growth and phase change are observed owing to the volatilization of Bi2O3. The varistor voltage decreased from 280 V/mm to 195 V/mm with the increase in sintering temperature, and the nonlinear coefficient (α) and leakage current of the varistor sintered at 1120 oC were 42.3 and 2.8 μA, respectively. For the varistor sintered at 1120 oC, the surface temperature and current increased from 45.3 oC to 87.9 oC and from 2.8 kA to 7.44 kA, respectively, under the surge voltage (waveform of 1.2/50 ms) of 6 kV to 15 kV. According to a repeated surge test (waveform: 1.2/50 ms and 8/20 ms, surge voltage 6.6 kV/3 kA, interval: 60 s), the varistor exhibited excellent surge-withstanding capability with the variation rate of voltage 0.8% and the variation rate of leakage current within 1.5%.

Keywords: Varistor, Sintering temperature, Nonlinear coefficient, Surge voltage.