Iron oxidation state of FeTiO3 under high pressure

The oxidation state of iron in FeTiO3 under high pressure was investigated by combining x-ray diffraction, Mossbauer spectroscopy, x-ray-absorption spectroscopy, and density-functional theory based calculations. Our results demonstrate that the ilmenite-to-perovskite phase transition occurs above 20 GPa at room temperature and on compression two phases coexist to 40 GPa. The Fe3+/Sigma Fe ratio increases up to 16 GPa, probably attributed to the d-electron drifting of cations via the oxygen bridge in the adjacent octahedral, then decreases at higher pressure due to the ilmenite-to-perovskite phase transition accompanied by a slight decrease in iron valence state. Our ab initio calculations further show that the most significant changes in the charge distribution in FeTiO3 are associated with Ti and O.