Sintering of Nanocrystalline Multicomponent Zinc Oxide Varistor Powders Prepared by Ball Milling

Abstract

Nanocrystalline ZnO–V2O5–MnO2–Nb2O5 varistor ceramic powder mixtures modified by different amount of Er2O3 addition (0-2 mol.%) have been prepared by high energy ball milling. Densification, microstructure and electrical characteristics of the ball milled precursor powders during isochronal sintering at 950 to 1250°C for 1 h as well as isothermal sintering for 0.25 to 2h at 1100°C have been investigated. Densification process is found to diminish slightly while growth of ZnO grain is reduced markedly with increasing Er2O3 addition due to the formation of Er-rich spinel phases at grain boundaries and triple points that restrict the grain boundary migration. It has been demonstrated that ultrafine grained multicomponent ZnO varistor ceramics can be achieved by simple conventional sintering via judicial selection of sintering time (≤ 1h) and temperature (≤ 1100°C) and amount of rare-earth oxide (Er2O3) addition (1.0 mol.%). ZnO varistor with 0.5 mol.% Er2O3 sintered at 1100°C for 0.5h exhibits best varistor property with breakdown field of 3880 Vcm-1.