The characteristics of ZnO-MnO2-Bi2O3-Co2O3-TiO2-based varistor ceramics doped with Sb2O3 and/or Cr2O3

The effect of Cr2O3 and Sb2O3 on the physical and electrical properties of ZnO-MnO2-Bi2O3-Co2O3-TiO2-based varistors ceramics were investigated in this work. The microstructure and electrical properties of varistors, which are composed of ZnO-MnO2- Bi2O3- Co2O3-TiO2-based varistors ceramics, were investigated in the range of (0.04 - 0.2) mol% Cr2O3 samples (B1 , B2 & B3 ) and 0.12 mol % of both Cr2O3 and Sb2O3 sample (Z1) or 0.12 mol% Cr2O3 and 0.06 mol% Sb2O3 (Z2). All samples exhibit non-linear current-voltage behavior. Addition of Bi2O3 in present of Co2O3, MnO2, Sb2O3 and Cr2O3 lead better densification by minimizing the present of closed pores. Also maximum values of firing shrinkage were attained in specimens fired at 1220 ?C for 2 hours. SEM of mix B1, shows two phase, ZnO grains and intergranular phase triple point, and TiO2, Co2O3 and Cr2O3 go into solid solution in the ZnO grains. Also Bi-rich phase in the triple point and increase the presence of liquid phase (melt liquid phase) on the grain boundary. The relation between I and V for the different mixes show very good plateau in (I-V) relation.