Effect of CuO addition on the microstructure and electrical properties of SnO2-based varistor

The effect of CuO addition on the properties of (Co, Nb, Cr)-doped SnO2 varistors were investigated. The samples with different CuO concentrations were fabricated by the conventional ceramic method and sintered at 1,200, 1,250, 1,300 and 1,350 °C for 2 h. It is found that the nonlinear coefficient presents a peak value at 0.2 mol % CuO addition. The leakage current density decreases with increasing CuO from 0 to 0.2 mol %, and then increases when the concentration of CuO is above 0.2 mol %. The breakdown electrical field decreases from 356 to 248 V/mm with increasing CuO from 0 to 0.6 mol %. The optimal samples obtained by doping CuO with 0.2 mol % and sintered at 1,300 °C have the highest nonlinear coefficient value of 31 and the lowest leakage current density of 2 μA/cm2.