Improving electrical properties of ZnO–Bi2O3–Sb2O3–MnO2 varistors by doping with pre-synthesized Bi–Si–O phase

Abstract The electric properties and microstructure of ZnO -Bi2O3– Sb2O3– MnO2 (ZBSM) varistor ceramics as a function of pre-synthesized mixture of 6Bi2O3 SiO2 (Bi–Si–O) were investigated. The introduction of Bi–Si–O increases liquid phase content during the sintering process, accelerating the solid solubility of MnO2, Sb2O3 and possibly partial Si ions towards ZnO grains. As results, the interface state density significantly increases to 16.43 × 1016/m2 in the 4 wt% Bi–Si–O ZBSM ceramic, which leads to the highest value of barrier height of 5.87 eV and nonlinear coefficient of 54.56. At the same time, the electric breakdown voltage and leakage current density decreases to 613.82 V/mm and 0.001 μA mm−2, respectively. Besides, grain boundary resistance gradually increases with increasing Bi–Si–O dopant (x ≤ 4 wt%) and then decreases sharply to a very low value when x = 6 wt%, which consists with the variation of leakage current density. Furthermore, only one relaxation occurred in ZBSM-xBi-Si-O varistors which can be confirmed by the Cole-Cole plot analysis. Oxygen absorption and ion migration mechanisms are used to explain the enhancement of nonlinear electrical properties.