Effect of aluminum addition on electrical properties, dielectric characteristics, and its stability of (Pr, Co, Cr, Y)- added zinc oxide-based varistors

The electrical properties, dielectric characteristics, and its stability against d.c. accelerated aging stress of (Pr, Co, Cr, Y)-added zinc oxide-based varistors were investigated for different aluminum concentrations under a sintering temperature of 1280 deg C. As the aluminum concentration increased, the average grain size (d) increased in the range of 4.3-5.5 μm and the sintered density increased in the range of 5.63-5.67 g/cm3. As the aluminum concentration increased, the breakdown field decreased in the range of 6327-710 V/cm and the maximum nonlinear coefficient (46.9) was obtained for 0.005 mol% in aluminum concentration, further additions impaired the nonlinear properties. As the aluminum concentration increased, the apparent dielectric constant increased in the range of 500.5-1327.4 and dissipation factor increased in the range of 0.00493-0.0724. The varistor added with 0.001 mol% Al exhibited the highest stability for E-J characteristics in which %ΔE1mA is +1.4% and %Δα is -5.7%, under stress state of 0.95 E1mA/150 deg C/24 h. (author)