(Gd, Co, Ta)-Doped SnO2 Varistor Ceramics

The effect on the microstructure and electrical properties of (Co, Ta)-doped SnO2 varistors upon the addition of Gd2O3 was investigated. The threshold electric field of the SnO2 based varistors increased significantly from 720 V/mm to 1455 V/mm, the relative dielectric constants of the SnO2 based varistors decreased greatly from 833 to 330 as Gd2O3 concentration was increased up to 1.2 mol%. The significant decrease of the SnO2 mean grain size, from 3.8 to 1.6 μ m with increasing Gd2O3 concentration over the range of 0 to 1.2 mol%, is the origin for increase in the threshold voltage and decrease of the dielectric constants. The mean grain size reduction is attributed to the segregation of Gd2O3 at grain boundaries hindering the SnO2 grains from conglomerating into large particles. Varistors were found to have superhigh threshold voltage and comparatively large nonlinear coefficient α . For 0.8 mol% Gd2O3-doped sample, threshold electrical field E and nonlinear coefficient α were measured to be 1125 V/mm and 24.0, for 1.2 mol% Gd2O3-doped sample, E and α were 1355 V/mm and 23.0. Superhigh threshold voltage and large nonlinear coefficient qualify the Gd-doped SnO2 varistor as an excellent candidate in use for high voltage protection system.