Charge order, orbital order, and electron localization in the Magneli phase Ti4O7

TL;DR

This study investigates the metal-insulator transition in Ti4O7, revealing that it results from a complex interplay of charge order, orbital order, and singlet formation in Ti 3d states, combining features of Fe3O4 and VO2.

Contribution

It provides a detailed electronic structure analysis showing the combined roles of charge and orbital order in Ti4O7's transition, linking it to mechanisms in Fe3O4 and VO2.

Findings

Charge order resembles Verwey transition in Fe3O4

Orbital order and singlet formation are similar to VO2

Transition involves complex interplay of charge and orbital effects

Abstract

The metal-insulator transition of the Magneli phase Ti4O7 is studied by means of augmented spherical wave (ASW) electronic structure calculations as based on density functional theory and the local density approximation. The results show that the metal-insulator transition arises from a complex interplay of charge order, orbital order, and singlet formation of those Ti 3d states which mediate metal-metal bonding inside the four-atom chains characteristic of the material. Ti4O7 thus combines important aspects of Fe3O4 and VO2. While the charge ordering closely resembles that observed at the Verwey transition, the orbital order and singlet formation appear to be identical to the mechanisms driving the metal-insulator transition of vanadium dioxide.