Effect of erbium on varistor characteristics of vanadium oxide-doped zinc oxide ceramics

The effect of erbium addition on microstructure, electrical properties, and ageing behavior of vanadium oxide-doped zinc oxide varistor ceramics was systematically investigated. Analysis of the microstructure indicated that the ceramics added with erbium consisted of ZnO grain as a main phase and secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, ErVO₄, V₂O₅, and Mn-rich. The average grain size decreased from 5.5 to 5.2 μm up to 0.05 mol%, whereas a further addition gradually increased it to 5.7 μm at 0.25 mol%. The sintered density increased from 5.51 to 5.61 g/cm³ with an increase in the amount of Er₂O₃. With increasing the amount of Er₂O₃, the breakdown field increased from 4,800 to 5,444 V/cm up to 0.05 mol%, whereas a further addition decreased it to 4,061 V/cm at 0.25 mol%. The varistor ceramics added with 0.05 mol% Er₂O₃ additives induced excellent nonlinear properties, with nonlinear coefficient of 63.4 by properly adding the amount of Er₂O₃ (0.05 mol%). The study indicated that the erbium acted as a donor to increase the donor concentration with an increase in the amount of Er₂O₃.