Synthesis, structure and dielectric properties of nanocrystalline SnO2–CoO–Nb2O5 varistor doped with Cr2O3

Abstract

The effect of Cr2O3 on the microstructure and dielectric properties of SnO2 varistors doped with Nb2O5 and CoO was investigated. The density of ceramic samples was calculated and found increases from 6.6819 to 6.8704 g cm−3. It is observed in this figure that, independent of the Cr2O3 concentration, no other crystalline phase besides SnO2 is observed indicating that the system is single phase within the detection precision of the X-ray diffraction. The average crystallite size of the prepared samples using was estimated Scherrer’s equation. A scanning electron microscope (SEM) was utilized in order to study the effect of variation of Cr2O3 content and its impact on the microstructure and electric properties. The obtained results show that, as Cr2O3 concentration increases the dielectric permittivity increases and ac resistivity decreases and then increases and takes it maximum resistivity at 0.5 mol%. The compositional dependence of the dielectric permittivity and ac resistivity has been explained in the light of the SEM micrographs. The obtained results show also that the sample of 0.5 mol% of Cr2O3 has highest resistivity and consequently low dielectric loss. So, it can be used in some technological applications such as transformer and inductor cores.