Effects of Bi2O3 Addition in Micro- and Nanoscale on the Structural and Electrical Properties of Zn1-xBixO varistors

Abstract

Two similar sets of Zn1-xBixO ceramic varistors with various x values (0.00 ≤x≤ 0.20) have been prepared by using Bi2O3 additions with two different sizes. In the first set, Bi2O3 nanoparticles (≈200 nm) were used, while Bi2O3 microparticles (≈5 μm) were used in the second set. It was found that addition of Bi up to 5 % for both sets did not affect the wurtzite-type hexagonal structure of ZnO, but with increasing Bi above 5 %, some unknown lines were clearly observed in XRD spectra. The grain sizes are increased in both sets with increasing Bi content up to 2.5 %, followed by a decrease with further increase of Bi up to 20 %, and their values for microparticle additions were larger than that of the sets containing nanoparticle additions. Two nonlinear regions were formed in the I–V curves of ZnO due to Bi2O3 nanoparticle additions above 5 %. However, this behavior was completely absent in the samples containing Bi2O3 microparticles. Moreover, the breakdown field and nonlinear coefficient decreased with Bi2O3 addition up to 5 % for both sets, followed by an increase with further increase of Bi up to 20 %, and their values were higher for nanoparticle additions than that of microparticles. A reverse behavior was recorded for the electrical conductivity. The results have been discussed in terms of Bi2O3 nanosize grains which may be localized at the grain boundaries of ZnO ceramics.