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

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.