MS19-01 - Orbital Molecules in Oxides
Paul Attfield (University of Edinburgh, United Kingdom)
Orbital molecules are weakly bonded clusters of transition metal ions within an orbitally ordered solid.[i] The importance of these quantum states has become apparent in recent years following the discovery of ‘trimeron’ orbital molecules in the ground state of magnetite (Fe3O4).[ii] Determination of the full superstructure below the famous Verwey transition at 125 K showed that Fe2+/Fe3+ charge ordering occurs with a pronounced orbital ordering of Fe2+ states that leads to localization of electrons in the linear, three-Fe trimerons. Recent results on orbital molecule orders in doped magnetites including natural samples will be presented.[iii] Vanadium oxides also provide many examples of orbital molecule orders, associated with NTE (negative thermal expansion) in the orbital polymer material V2OPO4.[iv] Persistence of large orbital molecules to high temperatures is discovered in the spinels AlV2O4 [v] and the new analog GaV2O4.[vi] Electronic phase separation driven by trimeron formation has recently been reported in CaFe3O5.[vii] Finally, some recent results revealing the origin of the Verwey transition will be presented.[viii]
i. J. P. Attfield, APL Materials 2015, 3, 041510.
ii. M.S. Senn, J.P. Wright, J.P. Attfield, Nature 2012, 481, 173.
iii. G. Perversi, et al, Chem. Comm. 2016, 52, 4864.
iv. E. Pachoud,et al, J. Am. Chem. Soc. 2018, 140, 636.
v. A. J. Browne; et al. Phys Rev Mat 2017, 1, 052003.
vi. A. J. Browne; et al. Inorg. Chem. 2018, 57, 2815.
vii. K. H. Hong, et al Nature Comm. 2018, 9, 2975.
viii. G. Perversi, et al, submitted.