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 degrees C. As the sintering temperature increases, the Bi-rich insulator layer tends to widen, and the average grain size increases to 13.22 mu m. The switching field, breakdown strength (E-1mA), and nonlinear coefficient (alpha) increase, while the leakage current density (J(L)) decreases, because of an increase in barrier height (phi(B)). In addition, the sintering temperature promotes a decrease in the dielectric constant (epsilon(a)) and an increase in dielectric loss. The ZnO-Bi2O3 varistor ceramic sintered at 1000 degrees C exhibits excellent overall electrical properties, with a switching field of 228.04 V/mm, E-1mA of 379.76 V/mm, alpha of 6.02, J(L) of 140 mu A/cm(2), phi(B) of 0.39 eV, and epsilon(a) of 172.87 at 1 kHz.