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.