Study on the electrical and dielectric behaviour of Zn-substituted cobalt ferrialuminates

The structural, electrical and dielectric properties of the spinel ferrite system ZnxCo1-xFeAlO4 (x = 0.2-0.5) have been studied by means of various experimental techniques. Polycrystalline samples of this series have been prepared by the double sintering ceramic method. The structural parameters such as the lattice constant, x-ray density, pore fraction, cation distribution, interionic distances and polaron radius have been determined for better understanding of the electrical and dielectric behaviour. The compositional and thermal variations of the electrical properties have been studied by means of dc resistivity, thermoelectric power, I-V and C-V measurements. The electrical parameters such as the activation energy, Fermi energy, charge carrier concentration and mobility have been determined and a probable conduction mechanism in the system has been suggested. It is found that the ferrites are electronic conductors, and various results confirm the formation of small polarons. Current controlled negative resistance (CCNR)-type switching is observed in samples with x = 0.3-0.5. The dielectric behaviour of the systemhas been studied by measuring the dielectric constant, complex dielectric constant and conductivity in the frequency range 100 Hz-1 MHz at selected temperatures. The compositions exhibit normal dielectric behaviour, attributed to Maxwell-Wagner type interfacial polarization. Broadband dielectric spectroscopy in the form of an electric modulus has been applied to investigate the electrical spectroscopy in a wide temperature range. The results clearly indicate the presence of the non-Debye type of dielectric relaxation in these materials.