Ni–Cu–Co ferrite synthesized using the sol–gel method: effects of the Cr3+ ion concentration on its structural, electrical, and dielectric properties

In this paper, we have investigated the structural, electrical, and dielectric properties of Ni0.1Co0.5Cu0.4Fe2-xCrxO4 (x = 0 and 0.3) ferrites. Samples have been prepared by employing the sol–gel method. The X-ray diffraction data along with Rietveld refinement were used to assess the phase purity and the structural parameters of samples. The morphology and the grain size of the prepared ferrite nanocrystals were observed with scanning electron microscopy. At room temperature, the Raman spectra displayed active phonon modes. FTIR spectra revealed two principal absorption bands due to the stretching vibration of metal oxygen in tetrahedral and octahedral sites. With increasing of Cr3+ concentration, both Raman and FTIR spectra showed that all modes shifted to higher wavenumbers. The dielectric properties were investigated using impedance complex spectroscopy in the frequency region (100‒106 Hz) at different temperatures. The ac-conductivity for both studied compounds was well analyzed using the augmented Jonscher equation. The plots of both imaginary part of permittivity (ε″) and dielectric loss (tanδ) vs. frequency, exhibit a dielectric dispersion in our compounds at low frequencies. This is described according to the Maxwell–Wagner model in agreement with Koop’s theory. The modulus curve was used to interpret the relaxation behaviors of charge carriers. The Nyquist plots of impedance for both samples have been modeled using the same equivalent circuit which is formed by a three-element R-CPE connected in series.