Effect of gadolinia addition on varistor characteristics of vanadium oxide–doped zinc oxide ceramics

Abstract

The effect of gadolinia addition on microstructure, electrical and dielectric characteristics, and aging behavior of vanadium oxide–doped zinc oxide varistor ceramics was systematically investigated. The average grain size decreased from 5.6 to 5.2 μm with an increase in the amount of Gd₂O₃ up to 0.1 mol%, whereas a further increase caused it to increase to 5.7 μm at 0.25 mol%. The sintered densities decreased from 5.51 to 5.44 g/cm³ with an increase in the amount of Gd₂O₃. With increasing the amount of Gd₂O₃, the breakdown field increased from 4,800 to 5,365 V/cm up to 0.05 mol%, whereas a further increase decreased it to 4,781 V/cm at 0.25 mol%. The varistor ceramics modified with 0.05 mol% Gd₂O₃ exhibited excellent nonlinear properties, with 66.1 in the nonlinear coefficient, whereas a further increase caused it to decrease to 17.6 at 0.25 mol%. The gadolinium acted like a donor, based on the electron concentration increasing from 4.20 × 10¹⁷/cm³ to 7.38 × 10¹⁷/cm³ with an increase in the amount of Gd₂O₃.