Sintering and varistor characteristics of ZnO-Bi2O3 ceramics

Abstract

The sintering behavior of binary ZnO ceramics (containing 0.01–1 mol% of added Bi2O3) showed that densification in the initial stage of sintering and grain growth of the ZnO matrix are enhanced in the presence of a liquid Bi2O3 phase. Exaggerated grain growth of ZnO was observed above 1100 °C and in mixtures containing as low as 0.05 mol % Bi2O3. Volatilization loss of Bi2O3 during sintering affected the microstructure of the sintered ceramics and resulted in the loss of varistor property and return to Ohmic behavior and high conductivity (∼1 Ω−1 cm−1). A simple microstructural model which predicts that the minimum content of Bi2O3 required to maintain varistor behavior is proportional to the thickness of intergranular layer and inversely proportional to the average grain size of the ZnO.