Investigation of electrical properties of tantalum doped SnO 2 varistor system

Abstract

Ta 2O 5 doped SnO 2 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 SnO 2·ZnO·CoO ceramics cannot exhibit electrical nonlinearity. A small amount of Ta 2O 5 improves the nonlinear properties of the samples greatly. The height and width of the defect barriers were calculated. It was found that samples doped with 0.05 mol% Ta 2O 5 exhibit the highest density (98.5%), the lowest electric breakdown field ( E b = 1100 V/cm) and the highest coefficient of nonlinearity ( α = 11.5). The effect of Ta 2O 5 dopant could be explained by the substitution of Ta 5+ by Sn 4+. A grain-boundary defect barrier model for the SnO 2·ZnO·CoO·Ta 2O 5 varistor system was also introduced.