Bulk modulus and electron density distribution of high-pressure polymorphs of Fe-Ti-O minerals

Yamanaka, Takamitsu*; Hattori, Takanori   

Bulk modulus and electron density distribution of high-pressure polymorphs of Fe-Ti-O minerals (FeO magnetite, FeTiO ulvspinel, FeTiO ilmenite, FeTiO pseudobrokite) are investigated by X-ray and neutron diffraction. The vacant sites in the unit cell have much larger volumes than cation sites in the all structures. Cation site partly occupied by Ti atom shows a smaller than that of only Fe atom and the compressibility of unit cell increases with increasing Ti content. The compressibility of the vacant sites is close to that of unit cells, but are much smaller than that of the cation site. The structure changes such as high-low electron spin transition, Jahn-Teller effect and hybridization in the Fe-O bonds are elucidated by present high-pressure experiments. The hybridization in the octahedral cation site was observed by molecular orbital calculation and it brings the deformation of the octahedral cation site, which triggers structure changes in the high-pressure polymorphs.