Nonohmic properties of V/Mn/Nb/Gd co-doped zinc oxide semiconducting varistors with low-temperature sintering process

The microstructure and nonohmic properties of the ZnO–V2O5–MnO2–Nb2O5–Gd2O3 (ZVMNG) semiconducting varistors were systematically investigated at low sintering temperature. With increasing sintering temperature, the average grain size increased from 4.1 to 11.7 μm, the sintered densities decreased from 5.54 to 5.42 g/cm3, and the breakdown field decreased noticeably from 7138 to 920 V/cm. The sample sintered at 900 °C exhibited excellent nonohmic properties, which are 66.1 in the nonohmic coefficient and 77 μA/cm2 in the leakage current density.