Polarization and Ni content effects on structural properties, electrical conductivity, complex impedance and dielectric constant of Co-Mg-ferrites

Pechini sol-gel technique was used to prepare Mg0.6-xNixCo0.4Fe2O4 (x = 0, 0.2, 0.4 and 0.6)-ferrite materials. Then, X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy techniques are used to investigate the structural, morphological, electrical and dielectric properties. The X-ray diffraction patterns show that the prepared samples have a single phase. The SEM micrograph shows that the particle has an unchanging grain size distribution. Electrical measurements show that the DC conductivity is sensitive to temperature. Then, it is well noticed that the Mott and Davis law is governed by the small polaron hopping model. Also, impedance measurements show that the real part of impedance is extensively reduced when applying a voltage bias of V-p = 10 V. Such behavior can be related to the reduction of the available density of trapped charge. The results of Nyquist fitting are coherent with the electrical measurements according to which the sample with the highest DC conductivity possesses the lowest grain boundary resistance. Dielectric measurements confirm that the thermal evolution of the dielectric constant of the samples containing intermediary amounts of Ni (x = 0.2 and x = 0.4) is classical and show that the dielectric transition temperature is affected by polarization.