Microstructure, electrical properties, and dc aging characteristics of Tb4O7-doped ZnO-based varistors

The microstructure, electrical properties, and dc-accelerated aging characteristics of Tb4O7-doped ZnObased varistors were investigated for different Tb4O7 amounts and sintering temperatures. The sintered density increased with increasing Tb4O7 amount and sintering temperature. The average grain size decreased with increasing Tb4O7 amount and increased with increasing sintering temperature. The varistor voltage and nonlinear coefficient increased with increasing Tb4O7 amount and decreased with increasing sintering temperature. The stability was worse with increasing Tb4O7 amount for the varistors sintered at 1,300 C. The 0.5 mol% Tb4O7-doped varistors sintered at 1,350 C exhibited a good stability for dc-accelerated aging stress of 0.95 V1 mA/150 C/24 h.