Effects of Low-Temperature Sintering on Varistor Properties and Stability of VMCDNB-Doped Zinc Oxide Ceramics

The varistor properties and stability against dc-accelerated stress of V2O5-Mn3O4-Co3O4-Dy2O3-Nb2O5-Bi2O3 (VMCDNB)-doped zinc oxide ceramics sintered at 850-925 degrees C were investigated. Increasing the sintering temperature increased the average grain size from 4.6 to 8.7 mm and decreased the density of the sintered pellet density from 5.54 to 5.42 g/cm(3). The breakdown field decreased from 5919 to 1465 V/cm because of the increase in the average grain size. Zinc oxide ceramics sintered at 875 degrees C showed the highest nonlinear coefficient (43.6) and the highest potential barrier height (0.96 eV). Zinc oxide ceramics sintered at 850 degrees C showed the highest stability: the variation rate of the breakdown field was -2.0% and the variation rate of the nonlinear coefficient was -23.3%, after application of the specified stress (applied voltage/temperature/time).