The Effect of Sintering Temperature on the Microstructure and Electrical Properties of ZnO–Bi2O3 Varistor Ceramics

The effect of sintering temperature on the microstructure and electrical properties of ZnO–Bi2O3 varistor ceramics was studied in the present work. Results demonstrate that the Bi-rich phase ZnBi38O60 is generated at the ZnO grain boundaries in the prepared varistor ceramics over a range of 850–1000°C. As the sintering temperature increases, the Bi-rich insulator layer tends to widen, and the average grain size increases to 13.22 μm. The switching field, breakdown strength ( E_1mA ), and nonlinear coefficient (α) increase, while the leakage current density ( J_L ) decreases, because of an increase in barrier height ( φ_B ). In addition, the sintering temperature promotes a decrease in the dielectric constant ( ε_a ) and an increase in dielectric loss. The ZnO–Bi2O3 varistor ceramic sintered at 1000°C exhibits excellent overall electrical properties, with a switching field of 228.04 V/mm, E_1mA of 379.76 V/mm, α of 6.02, J_L of 140 μA/cm2, φ_B of 0.39 eV, and ε_a of 172.87 at 1 kHz.