Effect of Cr2O3 on the property and microstructure of ZnO–Bi2O3 varistor ceramics in different sintering temperature

The electrical property, phase transformation, and microstructure of Cr2O3 doped ZnO–Bi2O3–Sb2O3–Co2O3–MnO2 (ZBSCM)-based varistors were investigated for different sintering temperature. The structure and morphological modifications were analyzed by X-ray diffraction and scanning electron microscopy (SEM), respectively. Doping Cr2O3 could lower the decomposition temperature of the pyrochlore phase Zn2Bi3Sb3O14, resulting in more Bi2O3 rich liquid phase and spinel phase Zn7Sb2O2. The results indicated that Cr2O3 played multiple roles in the grain growth and microstructure. Cr2O3 which acted as an indirect sintering aid to promote the grain growth was an effective additive which contributed to lower sintering temperature of ZnO varistors.