Effect of the sintering temperature on the electrical properties of Y–Al-doped ZnO varistors

To investigate the relationship between the electrical properties of Y–Al doped ZnO varistors and sintering temperature, in this study, we measured the voltage–current characteristics and electrical performance parameters of samples sintered at ${1100}^{\circ }C$–${1300}^{\circ }C$. Scanning electron microscopy observations revealed that as the sintering temperature increased, the grain size grew significantly, leading to a reduction in voltage gradient. Through $C\text{--}V$ characteristic testing, X-ray diffraction and energy dispersive X-ray spectroscopy analysis, it was found that the increase in sintering temperature promoted the formation of interface negative charge and defect reactions by $Y^{3+}$, increasing $N_i$ and $N_d$; ${\mathrm{Al}}^{3+}$ tends to aggregate in the grain area, further increasing $N_d$; the volatilization of ${\mathrm{Bi}}^{3+}$ gradually increases, causing a decrease in $N_i$; the ${\Phi }_b$ first increases and then decreases with the changes in $N_i$ and $N_d$, resulting in a U-shaped variation characteristic of the nonlinear coefficient and leakage current density. At a sintering temperature of ${1200}^{\circ }C$, the performance of ZnO varistors is optimal.