Effect of Cu ion substitution on structural and dielectric properties of Ni–Zn ferrites

A series of Cu-substituted Ni0.5–xCuxZn0.5Fe2O4 (x=0.12, 0.16, 0.20, 0.24 and 0.28) spinel ferrites were prepared by conventional ceramic method to investigate the effects of Cu compositional variation on the structure and dielectric properties. XRD patterns demonstrate that all the samples are crystallized in single-phase cubic spinel structure and the lattice constant increases with increasing Cu content. White grains observed by SEM are Cu-rich phase. The dielectric constant versus frequency curve displays a normal dielectric behavior of spinel ferrites. While the frequency dependence of dielectric loss tangent is found to be abnormal, exhibiting a peak at certain frequency for all Cu-substituted Ni–Zn ferrites. A maximum of the resistivity is observed at x=0.2 due to the decrease of hopping electrons between Fe2+ and Fe3+ in per unit volume, which is in contrast with the Cu content dependence of dielectric constant and dielectric loss.