Experimental study of electrical and dielectric properties of Cu0.6Mg0.2Co0.2FeCrO4 spinel ferrite

Abstract

This paper investigates the physical properties of Cu_0.6Mg_0.2Co_0.2FeCrO₄ spinel ferrite produced by the sol-gel method and calcined at 850 °C. Our specimen possesses a cubic structure with \(Fd\bar{3}m\) space group. We detect the presence of small amount of Fe₂O₃. Our sample exhibited lattice parameters where a, b, and c were all equal to 8.3506 Å, and the cell volume was 582.307 ų. Then, the spectrum demonstrated good refinement analysis, with a χ² factor of 1.66. Subsequently, the Debye–Scherrer equation provided a grain size of 88.18 nm. However, the grain size determined by the Williamson-Hall method resulted was 96 nm. Morphological analysis indicated that our sample consists of micro-sized grains equal to 2.62 µm. The dielectric analysis was carried out from 300 to 600 K, while measurements were taken over a wide frequency range from 10² to 10⁶ Hz. Examination of the relaxation time and AC conductivity revealed that the same charge carriers could be responsible for both the relaxation and conduction mechanisms. The increase in conductivity at high-frequency can be attributed to the influence of charge carrier mobility through different localized states. This force also promotes the release of confined charges from different trapping sites. The overlapping-large polaron tunneling (OLPT) and Correlated Barrier Hopping (CBH) models were utilized to clarify the observed conduction mechanism. Furthermore, at lower frequencies, the sample exhibited higher real impedance values. Then, as the frequency rose, the Z′ values decreased because more charge entities were transported, leading to a reduction in the concentration of trapped electric charge. The changes observed in Z″ suggest the emergence of the relaxation process. The Nyquist diagram was adjusted from 0 to 5 × 10⁷ to understand the equivalent circuit in our system. Then, the conduction mechanism in the sample is influenced by the contributions of both grain and grain boundaries. At low frequencies, the ε′ and ε″ values showed a significant rise and gradually decreased with increasing frequency, indicating that the sample is suitable for high-frequency applications. The decrease in ε′ and ε″ values was more pronounced at lower frequencies than at higher frequencies. This behavior can be adequately explained using Maxwell and Wagner’s expression, which is in line with Koops’ theory, providing a coherent justification for the observed trends. The value of M′ rose with frequency independently of temperature, approaching a plateau at a maximum asymptotic value. This saturation phenomenon indicates that charge carriers move over short distances during the conduction process. The Kohlrausch, Williams, and Watts functions were used to fit imaginary electrical modulus spectra. This revealed the non-Debye nature of the relaxation mechanism in the material.

Graphical Abstract