Octahedral Symmetry Modification Induced Orbital Occupancy Variation in VO₂

Octahedral symmetry is one of the parameters to tune the functional properties of complex oxides. VO2, a complex oxide with a 3d1 electronic system, exhibits an insulator-metal transition (IMT) near room temperature (∼68 °C), accompanying a change in the octahedral structure from asymmetrical to symmetrical. However, the role of octahedral symmetry in VO2 on the IMT characteristics is unclear. Crystal and electronic structure analyses combined with density-functional-theory calculations showed the bandwidth-controlled IMT characteristics of monoclinic VO2 with high octahedral symmetry. The expanded apical V-O length for a high octahedral symmetry of a VO2 film increased the bandwidth of the conduction band by depressing V 3d-O 2p hybridization. As a result, the interdimer hopping energy increased and thereby decreased the IMT temperature, although the short V-V chain enhanced electron correlation. These findings suggest that octahedral symmetry can control the IMT characteristics of VO2 by changing the orbital occupancy.