Effect of sintering process on electrical properties and ageing behavior of ZnO–V2O5–MnO2–Nb2O5 varistor ceramics
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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 °C. The sintered density decreased from 5.52 to 5.44 g/cm3 and the average grain size increased from 4.4 to 9.6 μm with the increase of sintering temperature. The breakdown field (E1 mA) decreased from 6991 to 943 V/cm with the increase of sintering temperature. The ZVMN varistor ceramics sintered at 900 °C led to surprisingly high nonlinear coefficient (α = 50). The donor concentration (Nd) increased from 3.33 × 1017 cm−3 to 7.64 × 1017 cm−3 with the increase of sintering temperature and the barrier height (Φb) exhibited the maximum value (1.07 eV) at 900 °C. Concerning stability, the varistors sintered at 925 °C exhibited the most stable accelerated ageing characteristics, with %ΔE1 mA = 1.5% and %Δα = 13.3% for DC accelerated ageing stress of 0.85 E1 mA/85 °C/24 h.