Simultaneously enhanced electrical stability and nonlinearity in ZnO varistor ceramics: Role of Si-stabilized δ-Bi₂O₃ phase

In the present study, simultaneously enhanced electrical stability (low degradation rate of 8.0 × 10⁻³ mA∙ h^1/2) and high nonlinear coefficient of 56 were obtained in ZnO varistors by doping SiO₂. To clarify the mechanism of enhanced properties, comprehensive microscopic analyses were studied. Particularly, the intrinsic point defects were quantitatively characterized for the first time. Results showed that the densities of zinc interstitials (Zn_i) and oxygen vacancies (V_o) were dramatically decreased, resulting in enhanced stability. Besides, reduced Zn_i and V_o decreased the total donor density, contributing to the improved barrier height and thus leading to enhanced nonlinearity. Combined with XRD and SEM results, it is deduced that such reduced Zn_i and V_o are attributed to the Si-stabilized high oxygen conducting δ-Bi₂O₃ phase. Furthermore, this elucidated mechanism, which has been long neglected in Si-doped varistors, may provide valuable insights into further developing high-performance ZnO varistors.