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°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 %ΔE _{1 mA} is +1.4% and %Δα is −5.7%, under stress state of 0.95 E _{1 mA}/150°C/24 h.