Effect of Al2O3 on the microstructure and electrical properties of WO3-based varistor ceramics

The influence of Al2O3 additive on the electrical properties and microstructure of (Na,Mn)-doped WO3 ceramics was studied. Addition of Al2O3 shifts the current–voltage characteristics to higher fields and inhibits the grain growth of the WO3-based non-Ohmic ceramics. The non-linearity coefficient of the current–voltage characteristics of the Al2O3-doped WO3 ceramics increases with sintering temperature and attains a maximum value at 1250°C.