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 ( \(E_{{1{\text{mA}}}}\) $E_{1\text{mA}}$ ), and nonlinear coefficient (α) increase, while the leakage current density ( \(J_{L}\) $J_L$ ) decreases, because of an increase in barrier height ( \(\varphi_{B}\) ${\phi }_B$ ). In addition, the sintering temperature promotes a decrease in the dielectric constant ( \(\varepsilon_{a}\) ${\epsilon }_a$ ) 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, \(E_{{1{\text{mA}}}}\) $E_{1\text{mA}}$ of 379.76 V/mm, α of 6.02, \(J_{L}\) $J_L$ of 140 μA/cm², \(\varphi_{B}\) ${\phi }_B$ of 0.39 eV, and \(\varepsilon_{a}\) ${\epsilon }_a$ of 172.87 at 1 kHz.