Conductivity and dielectric studies of copper–aluminate substituted spinel nickel ferrite

Abstract

Abstract Effect of Cu substitution in the spinel ferrite Ni 1− x Cu x Al 0.6 Fe 1.4 O 4 (0.0 ≤ x ≤ 1.0) in steps of 0.25 has been studied. Electrical measurements in the frequency range 10 2 –10 5 Hz and at temperature between 300 and 600 K show that these materials have a semiconductor-to-metallic transition as copper content increases. All studied compositions exhibit a transition with a change in the slope of the conductivity versus temperature curve. Dielectric parameters of these materials were studied as a function of frequency and temperature, where the dielectric permittivities ( ɛ ′, ɛ ″) revealed a dielectric anomaly at the transition temperature T c . The obtained T c is found to decrease with increasing Cu concentration. Relaxation spectrum was obtained in the relation of dielectric loss tangent (tan δ ) with frequency for sample with ( x = 0.5) where relaxation time τ and the maximum frequency ν ∞ of the hopping conduction mechanism is obtained. The variation of ( ɛ ′, ɛ ″ and tan δ ) with frequency and temperature displays a strong dependence on both nickel and copper concentrations. The results are explained in light of the cation–anion–cation and cation–cation interactions over the octahedral site in the spinel structure.