Effect of sintering process on electrical properties and ageing behavior of ZnO-V2O5-MnO2-Nb2O5 varistor ceramics

The effect of sintering process on microstructure, electrical properties, and ageing behavior of ZnO-V2O5-MnO2-Nb2O5 (ZVMN) varistor ceramics was investigated at 875-950 A degrees C. The sintered density decreased from 5.52 to 5.44 g/cm(3) and the average grain size increased from 4.4 to 9.6 mu m with the increase of sintering temperature. The breakdown field (E-1 mA) decreased from 6991 to 943 V/cm with the increase of sintering temperature. The ZVMN varistor ceramics sintered at 900 A degrees C led to surprisingly high nonlinear coefficient (alpha A = 50). The donor concentration (N-d) increased from 3.33 x 10(17) cm(-3) to 7.64 x 10(17) cm(-3) with the increase of sintering temperature and the barrier height (I broken vertical bar(b)) exhibited the maximum value (1.07 eV) at 900 A degrees C. Concerning stability, the varistors sintered at 925 A degrees C exhibited the most stable accelerated ageing characteristics, with %Delta E-1 mA = 1.5% and %Delta alpha = 13.3% for DC accelerated ageing stress of 0.85 E-1 mA/85 A degrees C/24 h.