Effects of CuO on the grain size and electrical properties of SnO2-based varistors

The effects of CuO on the SnO2·Co2O3·Ta2O5 varistor system sintered at 1250 °C for 80 min were investigated. It was found that CuO significantly affects the grain size and electrical properties of the SnO2-based varistors. The grain size rises from 4.7 to 11.4 μm, the breakdown electrical field decreases from 485 to 265 V mm−1 and relative dielectric constant (at 1 kHz) increases from 970 to 2451 with an increase in CuO concentration from 0.00 to 1.00 mol%. The sample with 0.25 mol% CuO has the best nonlinear electrical property and the highest nonlinear coefficient (α = 15.7) among all samples. The reason why grain size increases with increasing CuO concentration is explained. Also, the interpretation of the increase in nonlinearity is given.