Investigation of electrical properties of tantalum doped SnO2 varistor system

Ta2O5 doped SnO2 varistor systems containing 0.5 mol% ZnO and 0.5 mol% CoO were prepared by mixed oxide method. Considering that ZnO and CoO oxides are densification additives only the SnO2.ZnO.CoO ceramics cannot exhibit electrical nonlinearity. A small amount of Ta2O5 improves the nonlinear properties of the samples greatly. The height and width of the defect barriers were calculated. Samples doped with 0.05 mol% Ta2O5 exhibit the highest density (98.5%), the lowest electric breakdown field (Eb = 1100 V/cm) and the highest coefficient of nonlinearity (alpha = 11.5). The effect of Ta2O5 dopant could be explained by the substitution of Ta5+ by Sn4+. A grain-boundary defect barrier model for the SnO2.ZnO.CoO.Ta2O5 varistor system was also introduced. 18 refs.