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).