Effect of Ce³⁺ substitution on the structural, morphological, dielectric, and impedance spectroscopic studies of Co–Ni ferrites for automotive applications

Abstract

Cerium (Ce³⁺)-substituted cobalt–nickel (Co–Ni) ferrite nanostructures of spinel cubic phase with space group Fd$\bar{3}$m had been successfully engineered by solution combustion route. The effect of Ce³⁺ substitution on the structural, morphological, dielectric, and impedance spectroscopic investigations are probed by using X-ray diffraction (XRD), scanning electron microscope (SEM), and impedance analysis, respectively. Rietveld refinement of XRD data reveal that samples exhibit well-crystalline nature with single phase. The microstructural realm with various Ce³⁺ doping levels has been identified from SEM micrographs. The replacement of Fe³⁺ by Ce³⁺ cations has been confirmed by using energy-dispersive analysis of the ferrite samples. The dielectric constant (ε′), dielectric loss (tanδ), ac conductivity (σ_ac), and impedance (Z′ and Z″) at room temperature is investigated as a function of frequency, respectively. The variation of dielectric properties ε′, tanδ, σ_ac with frequency are explained by Maxwell–Wagner type of interfacial polarization and the hopping of charge between Fe²⁺ and Fe³⁺ as well as the dopant ions at B-sites. The decrease in dielectric constant and dielectric loss tangent with frequency follows the phenomenon of Debye’s relaxation. The enhancement in AC conductivity with frequency is proportional to Ce³⁺ concentration which follows Jonscher law. The complex impedance plots (Z′ vs. Z″) allows to determine the contribution for conductivity either from grain or grain boundary. Complex electric modulus plot (M′ vs. M″) provides the validation to the result drawn from the complex impedance plots. The results indicate the existence of non-Debye type of relaxation in these ferrites. Impedance spectroscopy allows the ferrite materials to estimate electrical properties which arise due to hopping and relaxation phenomena.