Improved varistor nonlinearity via sintering and acceptor impurity doping

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 alpha = 14 and E-0.5 = 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 degreesC 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 (Phi (B)). The experimental results were explained with the defect barrier model for SnO2-based varistors.