Effect of Co2O3 on the microstructure and electrical properties of Ta-doped SnO2 varistors

摘要

The effect of Co2O3 on the microstructure and electrical properties of Ta-doped SnO2 varistors was investigated. It was found that a sample doped with 0.1 mol% Co2O3 had the highest nonlinear coefficient alpha = 33, the highest breakdown electrical field E-B = 872 V mm(-1) and the lowest relative dielectrical constant epsilon(r) = 598 (measured at 1 kHz). However, 0.1 mol% Co2O3 is not sufficient for densification of SnO2 ceramics, and the relative density of the sample doped with 0.1 mol% Co2O3 (85.8%) is much lower than that of the samples doped with 0.3, 0.5, 0.8 and 1.2 mol% Co2O3 (about 98%). The highest breakdown electrical field and lowest relative dielectric constant of the sample doped with 0.1 mol% Co2O3 are mainly the result of the loose microstructure and the smallest average grain size. The measurements of grain boundary barrier height, Phi(B), and grain boundary resistance, R-GB, Indicate that Co-Sn(x) should be located at the depletion layer and is important to the formation of the grain boundary barrier.