Effects of Sc2O3 on the microstructure and varistor properties of (Co, Ta)-doped SnO2

The effects of Sc ₂O ₃ on the properties of (Co, Ta)-doped SnO ₂ varistors were investigated. It was found that the nonlinear coefficient presents a peak of α=19.3 for the sample doped with 0.05 mol% Sc ₂O ₃ . The breakdown electrical field increased from 303 to 1281 V/mm and relative dielectric constant decreased from 921 to 117 with increasing Sc ₂O ₃ from 0 to 0.09 mol%. The variations of breakdown electrical field and relative dielectric constant were mainly attributed to the decrease of SnO ₂ grain size, and mechanism of the decrease of SnO ₂ grain size was discussed. To illustrate the grain boundary barrier formation of (Sc, Co, Ta)-doped SnO ₂ varistors, a modified defect barrier model was introduced.