Structural, microstructural, and dielectric properties of Al, Ga, and Cr based high-entropy spinel oxides

Abstract

This study investigates the structural, microstructural, and dielectric properties of high-entropy spinel oxides with compositions (Ni_0.2Mg_0.2Co_0.2Cu_0.2Zn_0.2)B${}_2$O${}_4$, where B = Al, Ga, and Cr. X-ray diffraction (XRD) analysis confirms the formation of a single-phase cubic spinel structure (space group $Fd\bar{3}m$) for all compositions, with minor variations in lattice parameters and crystallite size attributed to the ionic radii and electronic configurations of the B-site cations. Field-emission scanning electron microscopy (FESEM) reveals uniform particle distributions with minimal agglomeration, indicating controlled microstructural characteristics. Dielectric properties were systematically examined using complex impedance spectroscopy over a frequency range of 100 Hz to 1 MHz. The frequency-dependent dielectric permittivity and tangent loss are explained by hopping charge polarization and defect dipole formation, with the modified Debye model effectively describing the relaxation processes. The results demonstrate that the dielectric properties are significantly influenced by the B-site cation, with Al and Ga-based samples exhibiting lower tangent loss, making them suitable for high-frequency applications, while Cr-based samples show higher tangent loss, indicating potential for energy absorption applications. These findings highlight the potential of high-entropy spinel oxides as advanced functional materials for tailored dielectric applications, offering insights into the role of configurational entropy and cationic disorder in optimizing material performance.