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

Effect of Cu substitution in the spinel ferrite Ni1−xCuxAl0.6Fe1.4O4 (0.0 ≤ x ≤ 1.0) in steps of 0.25 has been studied. Electrical measurements in the frequency range 102–105 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 Tc. The obtained Tc 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.