Microstructure and Electrical Properties of La2O3 and Sm2O3 Co-doped ZnO-Based Varistor Ceramics Prepared From Nanosize ZnO Powder

Abstract

High-performance ZnO–Bi2O3 varistors co-doped with a fixed amount of La2O3 and different amounts of Sm2O3 have been fabricated from nanosize zinc oxide powders by solid-state reaction. Phase composition, microstructure, and electrical properties were studied by x-ray diffractometry (XRD), scanning electron microscopy, and direct current electrical measurement. XRD analysis of the samples showed that a ZnO phase, a Bi2O3-rich phase, a spinel phase, and a pyrochlore-type phase were present; an Sm-rich phase was found in varistor ceramics containing large amounts of Sm2O3. The varistor ceramics had fine microstructures, and the corresponding grain size varied from 2.30 to 3.10 μm. Varistor ceramics doped with 0.1 mol% La2O3 and 0.5 mol% Sm2O3 then sintered at 1100°C for 2 h had good electrical properties (a breakdown field of 1130 V/mm, a nonlinear coefficient of 74, and a leakage current of 4.2 μA).