The metal-insulator transition of the Magnéli phase V4O7: Implications for V2O3

The metal-insulator transition (MIT) of the Magneli phase V4O7 is studied by means of electronic-structure calculations using the augmented spherical wave method. The calculations are based on the density-functional theory and the local density approximation. Changes of the electronic structure at the MIT are discussed in relation to the structural transformations occurring simultaneously. The analysis is based on a unified point of view of the crystal structures of all Magneli phase compounds VnO2n − 1 (3 ≤ n ≤ 9) as well as of VO2 and V2O3. This allows to group the electronic bands into states behaving similarly to the dioxide or the sesquioxide. In addition, the relationship between the structural and electronic properties near the MIT of these oxides can be studied on an equal footing. For V4O7, a strong influence of metal-metal bonding across octahedral faces is found for states both parallel and perpendicular to the hexagonal chex-axis of V2O3. Furthermore, the structural changes at the MIT cause localization of those states, which mediate in-plane metal-metal bonding via octahedral edges. This band narrowing opens the way to an increased influence of electronic correlations, which are regarded as playing a key role for the MIT of V2O3.