AC conductivity and frequency dependence of the dielectric properties for copper doped magnetite

A series of polycrystalline spinel ferrites with composition CuxFe3−xO4+δ (x=0.2, 0.4, 0.6, 0.8 and 1) were prepared by the standard ceramic method. The effect of Cu-ion substitution on the AC electrical conductivity and dielectric properties at different frequencies from 50 Hz up to 5 MHz was studied. The AC conductivity results were discussed in terms of the electron hopping model. The dispersion of the dielectric constant was discussed in the light of Koops' phenomenological theory and the Rezlescu model. The dielectric loss tangent tanδ curves exhibit dielectric relaxation peaks which are attributed to the coincidence of the hopping frequency of the charge carriers with that of the external fields. The frequency exponent factor (S) was estimated and it was found to vary between 0.4 for x=1 (CuFe2O4) and 0.83 for x=0.2.