Microstructural Morphology and Electrical Properties of Copper‐ and Niobium‐Doped Tin Dioxide Polycrystalline Varistors

The influence of a Nb 2 O 5 additive on the densification, microstructural morphology, and nonlinear electrical properties of the CuO‐doped SnO 2 ‐based varistors was investigated. It was found that copper oxide significantly improves the densification of the SnO 2 ceramics. The effects of Nb 2 O 5 on tin dioxide varistors were analyzed by X‐ray diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, and capacitance–voltage measurements, as well as impedance spectroscopy. Copper oxide segregates at the grain boundaries and precipitates at triple points, and niobium makes the tin dioxide grain semi‐conductive. The copper oxide intergranular insulating layer separates two semi‐conductive tin dioxide grains and forms the barriers. The reason for the nonlinearity of SnO 2 ‐based ceramics was explained.