Understanding Disorder-driven Metal-Insulator Transitions in Heteroanionic TiOF

Temperature-driven metal insulator transitions (MITs), occurring when the metallic state transforms into an insulating state at lower temperatures, or vice versa, hold great potential for applications in next-generation electronic devices. The underlying interactions governing the MITs in oxides arise from a combination of factors: electronic correlations, metal-metal bonding and lattice distortions (dimerization) cooperatively interact to drive the transition. Here, we investigate the behavior of the rutile-structured heteroanionic oxyfluoride TiOF using first principles simulations as a route to disentangle various contributions to MITs in the d¹ rutile family. We first model the structure of TiOF using edge-sharing fac ordered [TiO₃F₃] heteroleptic units and explore the effects of magnetism and electron correlation. We also construct a cluster expansion model to understand the interactions that govern the short- and long-range anion order in TiOF and its consequence on the observed insulating and paramagnetic behavior, demonstrating the robustness of our method in disentangling the dependencies of electronic and magnetic properties on these parameters. Ultimately, our work provides improved understanding on anion ordering tendencies in heteroanionic MIT materials and offers insights on synthetically achieving anion order on length scales necessary for device applications.