Exploring the Electronic Nature of Spinel Oxides: A Review of Their Electron Interactions and Prospects

Abstract: This review discusses the multifaceted electronic properties of spinel oxides with a particular focus on Lithium Vanadate (LiV2O4), Lithium Titanate (LiTi2O4), and Magnesium Titanate (MgTi2O4). We selected LiTi2O4, LiV2O4, and MgTi2O4 because they serve as quintessential examples of spinel oxides' diverse and intriguing electronic phenomena. LiV2O4 heavy fermion behaviour challenges traditional theories in d-electron systems, LiTi2O4 being the first oxide superconductor provides critical insights into unconventional superconductivity driven by strong electron-phonon interactions, and MgTi2O4 pronounced orbital ordering and metalinsulator transition offers a clear model for exploring electron-lattice coupling. This shows how the inherent structural versatility of the spinel lattice, characterised by its cubic close-packed oxygen network and variable cation distributions, enables a rich interplay of electron-electron correlations, electron-lattice coupling, and orbital degrees of freedom. In LiV2O4, the combination of mixed-valence vanadium ions and a geometrically frustrated pyrochlore lattice gives rise to heavy fermion behaviour, whereas LiTi2O4 exhibits unconventional superconductivity driven by a high density of states at the Fermi level and strong electronphonon interactions. MgTi2O4 undergoes a pronounced metal-insulator transition, where orbital ordering triggers a Peierls-like distortion that stabilises a low-temperature insulating state through Ti-Ti dimerization. How the composition of these compounds affects their properties, based on both theoretical research and experimental findings, is illustrated by this review. It illustrates the promise of Spinels in practical technologies such as energy storage, electrocatalysis, and high-temperature lubrication.