Effects of the substitution by copper on structural, optical and dielectric properties of the spinel LiFe2O4

Abstract

Spinel lithium ferrites are of great importance in fields of technological applications. Their characteristics are subject to several studies to investigate the involved mechanisms. We prepared the spinel Li0.2Cu0.8Fe2O4-d ferrite by the solid-state method and we studied the effect of copper incorporation. X-ray diffraction confirms the Li0.2Cu0.8Fe2O4-d compound crystallizes with a cubic spinel structure with space group Fd3‾m. The morphology micrograph shows that the grains are agglomerated in asymmetrical formations. Nyquist plots exhibits significant contribution of grains and grain boundaries. Both modulus and impedance results confirm that Li0.2Cu0.8Fe2O4-d sample exhibits a Cole-Cole relaxation type. The AC conductivity variation shows a dispersive behavior governed by the jump relaxation model. Hopping conduction is explained by two theoretical models. The first is attributed to the correlated barrier-hopping model at low temperature, and the second corresponds to the non-overlapping small polaron tunneling mechanism at high temperature. The dielectric behavior shows a polarization effect. Optical properties show that the band gap value is equal to 1.47 eV. Finally, the magnetization curve indicates that our sample present a phase transition and evidences the presence of ferromagnetic behavior.