Effect of Frequency and Temperature on Dielectric and Transport Properties of CaO stabilized ZrO2@mullite composites

This study concerns the synthesis and structure related electrical property analysis of CaO doped ZrO₂@mullite composites. Two synthesis techniques (solid state reaction route and thermal plasma sintering) are used which results the formation of a composite consisting of mixed phase of orthorhombic mullite, tetragonal and monoclinic zirconia. The lattice parameters, residual strains, average crystallite size and cell volume of these CaO-doped ZrO₂@mullite composites are obtained from XRD analysis. Stabilization of t-ZrO₂ phase at room temperature is confirmed. Porous microstructure observed in SEM images results in low dielectric constant value of these composites. At room temperature and selected frequency of 1MHz, the dielectric constant and loss factor of 4.7 and 3.826 × 10⁻² is observed for conventional CaO stabilized ZrO₂@mullite composite and that of 3.8 and 2.19 × 10⁻² is reported for plasma sintered CaO stabilized ZrO₂@mullite composite. The impedance spectroscopic analysis demonstrates the negative temperature coefficient of resistance (NTCR) behavior and non-Debye type relaxation behavior of both the CaO stabilized ZrO₂@mullite composites. A negligible effect of electrode polarization is realized in these composites. The electronic band gap of conventional and plasma sintered CaO stabilized ZrO₂@mullite composites is found to be around 3eV.