AC conductivity and dielectric behavior of CoAlxFe2-xO4

AC conductivity and dielectric properties have been studied for a series of polycrystalline spinel ferrite with composition CoAlxFe2-xO4, as a function of frequency and temperature. The results of AC conductivity were discussed in terms of the quantum mechanical tunneling and small polaron tunneling models. The dispersion of the dielectric constant was discussed in the light of Koops model and hopping conduction mechanism. The dielectric loss tangent tan 5 curves exhibits a dielectric relaxation peaks which are attributed to the coincidence of the hopping frequency of the charge carriers with that of the external fields. The AC conductivity, dielectric constant, and dielectric loss tangent were found to increase with increasing the temperature due to the increase of the hopping frequency, while they decrease with increasing Al ion content due to the reduction of iron ions available for the conduction process at the octahedral sites. (C) 2003 Elsevier SAS. All rights reserved.