Effect of Cr2O3 addition on the microstructure and electrical properties of SnO2-based varistor

The effect of Cr2O3 addition on the properties of (Co, Nb)-doped SnO2 varistors were investigated. The samples with different Cr2O3 concentrations were fabricated by the conventional ceramic method and sintered at 1,250, 1,300, 1,350 and 1,400 °C for 2 h. It was found that the nonlinear coefficient present a peak value when 0.05 mol % Cr2O3 was added. The leakage current density decreases with increasing Cr2O3 from 0 to 0.05 mol %, but increases when the concentrations increase from 0.05 to 0.07 mol %. The breakdown electrical field increased from 337 to 866 V/mm with increasing Cr2O3 from 0 to 0.07 mol %. The optimal samples obtained by doping Cr2O3 with 0.05 mol % and sintered at 1,300 °C have the highest nonlinear coefficient value of 27 and lowest leakage current density of 9 μA/cm2.