Charge order and spin-singlet pairs formation in Ti4O7

Abstract

Charge ordering in the low-temperature triclinic structure of titanium oxide (Ti4O7) is investigated using the local density approximation (LDA)+U method. Although the total 3d charge separation is rather small, an orbital order parameter defined as the difference between t2g occupancies of Ti${}^{3+}$ and Ti${}^{4+}$ cations is large and gives direct evidence for charge ordering. Ti 4s and 4p states make a large contribution to the static "screening" of the total 3d charge difference. This effective charge screening leads to complete loss of the disproportionation between the charges at 3+ and 4+ Ti sites. The occupied t2g states of Ti${}^{3+}$ cations are predominantly of $d_{xy}$ character and form a spin-singlet molecular orbital via strong direct antiferromagnetic exchange coupling between neighboring Ti(1) and Ti(3) sites, whereas the role of superexchange is found to be negligible.

6 pages, 4 figures

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• Effective Ising model for correlated systems with charge ordering
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• DFT+U simulation of the Ti${}_4$O${}_7$-TiO${}_2$ interface
• Electronic structure of the zigzag spin-chain compound In${}_2$VO${}_5$
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• Influence of germanium substitution on the structural and electronic stability of the competing vanadium dioxide phases
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