Orbital Molecules in the New Spinel GaV₂O₄

Abstract

The structures and properties of vanadium oxides are often related to the formation of molecule-like clusters of vanadium cations through direct V-V bonding. GaVO, a new vanadium spinel, was synthesized. Powder diffraction and X-ray total scattering studies, complemented by magnetization and resistivity measurements, reveal that the low-temperature phase of this material is structurally distorted and features ordered pairs of three- and four-atom vanadium clusters. These clusters persist into a disordered cubic phase above the charge-ordering transition at T = 415 K. Furthermore, quasi-elastic neutron scattering indicates that the disordered clusters remain well-defined and static to 1100 K.

Co-emergence of magnetic order and structural fluctuations in magnetite

“…Although the timescale for these structural fluctuations is not directly measured, their lack of correlation with phonon motions suggests that they are essentially static or slowly diffusing. A recent quasi-elastic neutron scattering study of GaV 2 O 4 spinel above the 415-K charge-ordering transition found that structurally disordered orbital molecules remain well defined and without measurable dynamics up to 1100 K 16 .…”

“…Analysis of the interatomic pair distribution function (PDF) 11 derived from total X-ray scattering data is a simple method for exploring local structure that is highly sensitive to the displacements of metal atoms associated with the formation of orbital molecules, metal–metal-bonded clusters such as the trimerons observed in magnetite 12 . Persistence of orbital molecules far above their long-range electronic ordering transitions has been discovered from X-ray PDF studies of Li 2 RhO 4 13 , Li 2 RuO 3 14 , AlV 2 O 4 15 , and GaV 2 O 4 16 .…”

Structural study of the pressure-induced metal-insulator transition in LiV2O4

“…17+ heptamers) are found [8,9]. The isoelectronic material GaV 2 O 4 behaves similarly [10]. The orbital molecules in the R3m structures of these materials are defined by short V-V distances, and an EXAFS study of LiV 2 O 4 identified similar shortening above 12 GPa at 300 K [11].…”

Site-selective doping of ordered charge states in magnetite

“…The Fe 2+ sites within the Fe 2+ /Fe 3+ charge-ordered array show a combination of orbital ordering and bonding to two Fe neighbours to form linear three-atom trimeron units, spin-polarised orbital molecules 10 . Orbital molecules associated with charge ordering have also been reported in other materials, such as CuIr 2 S 4 11 , AlV 2 O 4 12,13 , GaV 2 O 4 14 and CaFe 3 O 5 15 . Complex charge orders may lead to spontaneous formation of structurally inequivalent cations of the same charge, for example, ordering of V 4+ /V 5+ over eight inequivalent sites in α′-NaV 2 O 5 16 , and notably in the Cc magnetite superstructure where charges are localised over sixteen distinct octahedrally coordinated sites, eight for Fe 2+ and eight for Fe 3+ .…”