AC resistivity and frequency dependence of the dielectric properties for Al doped NiCuZn ferrites

A series of polycrystalline spinel ferrites with composition Ni_0.27Cu_0.10Zn_0.63Al_xFe_2-xO₄ for x values ranging from 0.00 to 0.16 in steps of 0.04 and sintered at 1300°C have been prepared and investigated by the standard double sintering ceramic technique. The effect of Al-ion substitution on the AC electrical resistivity and dielectric properties at different frequencies from 100 Hz up to 120MHz was studied. The AC resistivity results were discussed in terms of the electron hopping model. The dispersion of the dielectric constant was discussed in the light of Koop´s phenomenological theory and Maxwell-Wagner interfacial polarization. The dielectric loss tangent exhibit dielectric relaxation peaks which are attributed to the coincidence of the hopping frequency of the charge carriers with that of the external fields. All the variations are explained on the basis of Cu²⁺ and Cu⁺; Ni²⁺ and Ni³⁺; Fe²⁺ and Fe³⁺ concentrations on octahedral sites and electronic hopping frequency between Fe²⁺ and Fe³⁺ ions and hole transfer between Cu²⁺ and Cu+; Ni²⁺ and Ni³⁺ over octahedral site.