Microstructure of Varistors Prepared with Zinc Oxide Nanoparticles Coated with Bi2O3

Abstract

Zinc oxide (ZnO) nanoparticles coated with 1–5 wt% Bi2O3 were prepared by precipitating a Bi(NO3)3 solution onto a ZnO precursor. Transmission electron microscopy showed that a homogeneous Bi2O3 layer coated the surface of the ZnO nanoparticles and that the ZnO particle size was ∼30–50 nm. Scanning electron microscopy showed that ZnO grains sintered at 1150°C were homogeneous in size and surrounded by a uniform Bi2O3 layer. When the ZnO grains were surrounded fully by Bi2O3 liquid phases, further increases in the ZnO grain size were not affected by the Bi2O3 content. This predesigned ZnO nanoparticle structure was shown to promote homogeneous ZnO grains with perfect crystal growth.