Effect of Sc2O3 on the electrical properties of (Co, Ta, Cr)-doped SnO2 varistors

The effects of Sc2O3 doping on the electrical properties of (Co, Ta, Cr)-doped SnO2 varistors were investigated and the maximal nonlinear coefficient (α=34) of the sample doped with 0.03 mol% Sc2O3 was obtained. It was found that the breakdown electrical field of samples increased significantly with increasing Sc2O3 concentration and the sample doped with 0.08 mol% Sc2O3 has the highest breakdown electrical field of 3336 V/mm. The measurement of grain size and sample impedances reveal that the increase of grain boundary resistance is the substantial reason for the increase of breakdown electrical field. The increase of grain boundary resistance may be caused by the increase of depletion layer thickness and it can be illustrated by the decrease of relative dielectric constant with increasing Sc2O3 concentration.