Microstructure development and nonlinear electrical characteristics of the SnO2·CuO·Ta2O5 based varistors
The microstructure development of SnO2·CuO based ceramic material was analyzed by XRD and SEM and the electrical properties were investigated by J-E relation. The secondary phases of copper oxide were found by the XRD. Copper oxide could make tin oxide densify and advance the grain growth, while tantalum oxide would retard the grain growth. Excess copper would centralize at the grain boundaries and prevent the mass transport. The high nonlinear coefficient (α = 27.3) and low leakage current density (JL = 16 μA cm−2) for the 0.05 mol% Ta2O5-doped SnO2·CuO based varistor sample were obtained. The modified defect barrier model for CuO and Ta2O5-doped SnO2 based varistors was introduced.