Low temperature sintering and characterization of 0.25–1 mol% Bi2O3 doped ZnBiMnNbO based varistor ceramics

Abstract The effect of Bi2O3 on the microstructure and properties of ZnO-based varistor ceramics sintered around 900 °C has not been fully understood. Therefore, ZnO (balanced)-x Bi2O3–2%MnCO3-0.1%Nb2O5 (x = 0.25, 0.5, 0.75 and 1%, all in molar ratio) varistor ceramics were prepared by solid-state sintering at 850–900 °C. Then, the effect of varying Bi2O3 concentration on the microstructure and nonlinear electrical properties of the as fabricated ceramic was studied by using XRD, SEM, EDS and conventional electric field-current density (E-J) test. The Results show that the Mn and Nb doping is the main reason for making Bi2O3 derived liquid phase capable of densifying the ZnBiMnNbO varistor ceramic at 850–900 °C. The sintered ceramics consist of ZnO and other three secondary phases:Bi2O3, Mn3O4 and Bi5Nb3O15. The increase of Bi2O3 can improve the grain growth of the ceramic up to 0.75mol%. The further addition of Bi2O3 slightly inhibits the growth of ZnO grains. As a result, the breakdown voltage first decreases from 633.83 to 403.63 V/mm with the increase of Bi2O3 up to 0.75mol%, then increases slightly to 439.71 V/mm with the further increase of Bi2O3 to 1mol%. The nonlinear coefficient reaches its maximum value (58.68) at 0.5 mol% Bi2O3 in the ceramic sintered at 900 °C. Meanwhile, the leakage current density is as low as 3.16 μA/cm2. This study provides a good reference for producing the ZnO-based varistors at low costs.