Effect of In2O3 doping and sintering on the electrical properties and the microstructure of (Co,Ta)-doped SnO2 varistors

Abstract The effects of In 2 O 3 doping and sintering temperature on the microstructure and electrical properties of (Co,Ta)-doped SnO 2 varistors were investigated and the maximal non-linear co-efficient of α  = 51 of the sample doped with 0.08 mol% In 2 O 3 sintered at 1350 °C was obtained. It was found that the breakdown electrical field and resistivity of grain boundaries increased significantly with increasing In 2 O 3 concentration or decreasing sintering temperature. The sample doped with 0.12 mol% In 2 O 3 sintered at 1350 °C has the highest breakdown electrical field of 2592 V/mm. The relative dielectric constant decreased with increasing In 2 O 3 concentration or decreasing sintering temperature. The decrease or increase of breakdown electrical field, increase or decrease of relative dielectric constant with altering In 2 O 3 concentration and sintering temperature is mainly attributed to the increase or decrease of the grain size. The mechanism of the variation of SnO 2 grain size was discussed.