Non-ohmic effect and pulse aging behavior of V/Mn/Co/Bi/Dy co-doped ZnO semiconducting varistors with sintering processing

We examined the effect of sintering on the microstructure, non-ohmic properties, clamping characteristics, and pulse aging behavior of V/Mn/Co/Bi/Dy codoped ZnO semiconducting varistors. The average grain size increased from 4.7 to 10.4 µm and the densities of the sintered pellets decreased from 5.47 to 5.37 g/cm3 with the increase in sintering temperature. The maximum non-ohmic coefficient (35.3) was obtained at a sintering temperature of 900 °C. Varistors sintered at 900 °C exhibited the best clamp characteristics, a clamp voltage ratio of 1.74–2.54 at a pulse current of 1–25 A. Varistors sintered at 925 °C exhibited the strongest electrical stability; variation rates for the breakdown field measured at 1.0 mA/cm2, for the non-ohmic coefficient, and for the leakage current density were 3.4%, 6.6%, and −11.2%, respectively, after application of a pulse current of 100 A.