Improved varistor nonlinearity via sintering and acceptor impurity doping

Abstract

A new varistor system of SnO2-Bi2O3-Nb2O5 was reported in this paper. The electrical field-current density characteristics of this system were investigated by doping different amounts of Bi2O3 and sintering the samples at various temperatures. It is found that adding 0.75 mol% Bi2O3 to Nb-doped SnO2 ceramic resulted in maximum nonlinear coefficient and breakdown voltage with α = 14 and E0.5 = 19 525 V/cm. To improve the density as well as the nonlinearity of this system, different amounts of Co2O3 were added. The optimal conditions for the best nonlinearity were 1300 °C with 0.03 mol% Co2O3 addition. Deviation from this doping content, toward either higher or lower Co2O3 content, causes the deterioration of I−V characteristics. It can be concluded that the incorporation of cobalt oxides into SnO2-based varistors improves the nonlinearity in the low and intermediate current density regions because of the increased barrier height . The experimental results were explained with the defect barrier model for SnO2-based varistors.