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.