Densification and grain growth of CuO-doped Pr6O11 varistors

The effect of CuO doping on the microstructure and electrical properties of Pr6O11 varistors was investigated. Samples were prepared by conventional ceramic techniques, and were sintered at 1150 °C in air for 2 h. The microstructure was investigated by scanning electron microscopy (SEM). The phases and chemical composition were analyzed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results indicated that CuO can promote the densification of the Pr6O11-based varistors to 95.8% of the theoretical density. CuO forms a solid solution with Pr6O11 up to 0.5 mol%, above which Pr2CuO4 precipitates in the grain boundary. From the I–V measurements, minor CuO doping can improve the nonlinear electrical properties. A further increase in CuO content induces a reduction in the nonlinear electrical properties due to the consumption of absorbed oxygen on the grain surfaces.