Influence of frequency, temperature and composition on electrical properties of polycrystalline Co_0.5Cd_xFe_2.5-xO₄ ferrites

Polycrystalline ferrites with general formula Co_0.5Cd_xFe_2.5-xO₄ (0.0≤x≤0.5) were prepared by sol-gel method. The dielectric properties ε′, ε″, loss tangent tan δ and ac conductivity σ_ac have been studied as a function of frequency, temperature and composition. The experimental results indicate that ε′, ε″, tan δ and σ_ac decrease as the frequency increases; whereas they increase as the temperature increases. These parameters are found to increase by increasing the concentration of Cd content up to x=0.2, after which they start to decrease with further increase in concentration of Cd ion. The dielectric properties and ac conductivity in studied samples have been explained on the basis of space charge polarization according to Maxwell and Wagner's two-layer model and the hoping between adjacent Fe²⁺ and Fe³⁺ as well as the hole hopping between Co³⁺and Co²⁺ ions at B-sites. The values of activation energies E_f for conduction process are determined from Arrhenius plots, and the variations in these activation energies as a function of Cd content are discussed. The complex impedance analysis is used to separate the grain and grain boundary of the system Co_0.5Cd_xFe_2.5-xO₄. The variations of both grain boundary and grain resistances with temperature and composition are evaluated in the frequency range 42 Hz-5 MHz.