Effect of TiO 2 doping on microstructural and electrical properties of ZnO–Pr 6O 11-based varistor ceramics

Abstract

The microstructural and electrical properties of ZnO–Pr 6O 11 based varistors, which are composed of ZnO–Pr 6O 11–Co 3O 4–TiO 2 with different doping amounts of TiO 2, were investigated. Through X-ray diffraction and scanning electron microscopy analyses, it was found that TiO 2 acted as an inhibitor of ZnO grain growth in varistor ceramics, resulting in the decrease of ZnO grain size with more TiO 2 doped, due to the formation of more second phases such as PrTiO 3, Zn 2TiO 4 and even Pr 2Ti 2O 7 at the grain boundaries, which would exert more intensive pinning effects on the ZnO grain growth. Doping with appropriate amount of TiO 2 can improve the nonlinear property, and decrease the leakage current of the as-prepared ZnO–Pr 6O 11 based varistors. The samples’ varistor voltage and nonlinear exponents can be enhanced till no more than 1.0 mol% TiO 2 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.