Probing the influence of cation distribution on the vibrational dynamics and phase transitions in Mg-doped zinc ferrites: Quantum mechanical study

The assignment of vibrational modes in spinel ferrites using infrared (IR) and Raman spectroscopy is a task of considerable complexity due to the intricate vibrational behavior exhibited by these materials. This complexity is further compounded by the presence of a variety of metal cations occupying distinct positions in the crystal lattice. In the present study, we have undertaken a detailed analysis of the vibrational spectrum of Mg–Zn ferrite utilizing an ab initio periodic quantum-mechanical approach. We employed a localized Gaussian-type function basis set in conjunction with the B3LYP hybrid Hamiltonian to achieve this. The obtained results indicate that the ground state of Mg–Zn ferrite is an open-shell system with a mixed structure, characterized by magnesium atoms predominantly occupying octahedral sites, zinc atoms at the tetrahedral site, and iron atoms distributed across both sites. We report a discernible free energy difference of 0.07 eV, which includes zero-point energy, corresponding to 812 K, between the antiferromagnetic ground state and a ferromagnetic arrangement within the normal structure. The variations in IR and Raman frequencies identified in this research, as compared to the existing literature, hold significant potential for determining the phase of Mg–Zn ferrites in experimental spectra. This advancement offers a vital step toward a deeper understanding of the vibrational properties and potential applications of these ferrites.