Investigations of microstructural and impedance spectroscopic properties of Mg_0.5Co_0.5Fe_1.6Al_0.4O₄ ferrite prepared using sol–gel method

Polycrystalline Mg_0.5Co_0.5Fe_1.6Al_0.4O₄ ferrite was prepared using sol–gel method. This sample was characterized by powder X-ray diffraction (XRD), Scanning electron microscopy, and impedance spectroscopy. XRD analysis combined with the Rietveld refinement confirmed the cubic-spinel structure (SG: Fd3 - m) for the prepared sample. Electrical conductivity obeying the Jonscher power law indicates that the prepared material exhibits semiconductor behavior, and the conduction process follows the “non-overlapping small polaron tunnelling, NSPT” model between neighbors’ sites. The behavior of dielectric constants such as permittivity and loss coefficient has been interpreted based on the Maxwell–Wagner’s theory of interfacial polarization. The curves of imaginary parts of impedance (Z″) and modulus (M″) show dielectric-relaxation phenomenon in the sample with activation energy near to that determined from the dc conductivity study. Nyquist plots (− Z″ vs. Z′) show a monotonic decrease in both grain resistance (R_g) and grain boundary resistance (R_gb) with increasing temperature such as R_gb ≫ R_g. This result confirms that the transport mechanism in Mg_0.5Co_0.5Fe_1.6Al_0.4O₄ compound is governed by the grain boundaries effect.