Electrical and dielectric properties of hard/soft CoFe₂O₄/Ni_0.3Cu _xZn _yFe₂O₄ (x, y ≤ 0.5) spinel ferrite nanofibers

Hard–soft CoFe₂O₄/Ni_0.3Cu_xZn_yFe₂O₄ (x, y ≤ 0.5) spinel ferrite nanofibers (H/S CFO/CuZnFO SFNFs) were synthesized via electro-spin. The main aim of this study is to investigate effect of co-substitution of transition metals of Cu and Zn on the dielectric features of H/S CFO/NiFO SFNFs. The microstructure and morphology of all products were studied by XRD, SEM along with EDX, TEM and HR-TEM. The dielectric features of all products were evaluated as a function of frequency, F (1 MHz–3 GHz), and temperature, T (20–120 °C). The T-dependent AC and DC conductivity of all products improved with T, in agreement with the semiconductor behavior. While AC conductivity revealed two regions as F-dependent and F-independent, DC conductivities exhibited Arrhenius-type behavior above and below the transition T. Thermally stimulated charge transfer model produced activation energies before and after transition T ranging between E_a = 78 and 297 meV, which is consistent with AC and DC conductivities. The dielectric loss, dielectric constant and dielectric loss tangent of all nanofibers decreased with the increase in F at all T. The Cole–Cole plots were used to analyze the effect of grain and grain boundary on conduction mechanism, and they displayed mainly only one incomplete semicircle signifying non-Debye behavior and domination of grain boundaries to the conduction mechanism. The dielectric parameters of all samples vary significantly with compositional ratio. The dielectric behaviors of H/S CFO/CuZnFO SFNFs are correlated with the conduction mechanisms based on grain-to-grain boundaries, clarified by Koop's model.