Enhancement in the long-term stability of ZnO varistor ceramics against DC aging by controlling intergranular phases

Herein, to enhance the long-term stability, ZnO varistor ceramics mixed with Bi2O3, Sb2O3, MnCO3, Co2O3, SiO2, and different concentrations of NiO (with 0, 0.3, 0.7, 1, 1.3, 1.6 mol%) were grown for controlling the Bi2O3 intergranular phase as α-Bi2O3 using a well-known ceramic process technology. The microstructure and crystalline phases were investigated using scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The electrical properties were evaluated using a high-voltage DC power supply, current pulse generator, oscilloscope, and impedance analyzer. Results from XRD patterns and TEM indicated that the NiO dopant enables the transition of δ- to α-Bi2O3 phase. Current density-electric field measurements revealed that NiO-doped ZnO ceramics have an increased breakdown field and decreased leakage current density. During DC aging, the power loss-aging time curves of NiO-doped ZnO ceramics with increased α-Bi2O3 phase showed a downward trend, indicating increased stability. The current research has revealed that improving the electrical stability of polycrystalline ceramics via intergranular phase control might be feasible for the emerging DC power-based aging applications.