Effect of TiO2 doping on microstructural and electrical properties of ZnO–Pr6O11-based varistor ceramics

The microstructural and electrical properties of ZnO–Pr6O11 based varistors, which are composed of ZnO–Pr6O11–Co3O4–TiO2 with different doping amounts of TiO2, were investigated. Through X-ray diffraction and scanning electron microscopy analyses, it was found that TiO2 acted as an inhibitor of ZnO grain growth in varistor ceramics, resulting in the decrease of ZnO grain size with more TiO2 doped, due to the formation of more second phases such as PrTiO3, Zn2TiO4 and even Pr2Ti2O7 at the grain boundaries, which would exert more intensive pinning effects on the ZnO grain growth. Doping with appropriate amount of TiO2 can improve the nonlinear property, and decrease the leakage current of the as-prepared ZnO–Pr6O11 based varistors. The samples’ varistor voltage and nonlinear exponents can be enhanced till no more than 1.0 mol% TiO2 doped. The maximal values of varistor voltage and nonlinear exponents acquired in this work were 90.2 V/mm and 15, respectively. The obtained materials might be much promising in application of varistors for devices working under low voltages.