R3: High-pressure science and deep Earth’s material

[R3-05] Anoisotropic electrical resistivity in FeTiO₃ ilmenite, compressibility and spin state under high pressure.

*Takamitsu YAMANAKA¹ (1. Chinese HPSTAR)

Keywords:FeTiO3 ilmenita, high-pressure neutron diffraction, electrical resistivity measurement, anisotropic electron super exchange, electron radial distribution

Neutron and synchrotron X-ray diffraction experiments perform precise analysis of the FeTiO₃ ilmenite structure. FeTiO₃does neither transform into perovskite nor LiNbO₃ structure phase under pressures up to 28 GPa. However, different compression curves of both FeO₆ and TiO₆ octahedra are observed below 8 GPa. FeO₆ is more compressive and flexible than TiO₆. TiO₆ octahedron is an extremely rigid body. Pressure dependence of electrical resistivity using single crystal proves that FeTiO₃ ilmenite shows an anisotropic electrical conductivity. The resistivity in the direction perpendicular to the c-axis decreases monotonously with increasing pressure. On the other hand the resistivity parallel to the c-axis shows the hallow-shape of the curvature. In three Fe-Fe, Ti-Ti and Fe-Ti atomic distances, the shortest Fe-Ti distance presents the highest electrical conduction and electron mobility of Fe²⁺Ti⁴⁺ and Fe³⁺Ti³⁺ by electron super exchange during compression between adjacent Fe and Ti cations.The electron localization around Fe and Ti atoms is clarified by maximum entropy measurement calculation. Electron configuration of Fe²⁺ (3d⁶) is more strongly changed than Ti⁴⁺ (3d⁰) under compression. The electron configuration of the former cation is related to the revolution of Jahn-Teller effect in the ligand field of C_3v molecular symmetry. The anisotropic electrical conductivity and non-uniform structure change of Fe-Ti interatomic distance can be explained by the possible spin transition. The spin transition of FeKb from high-spin state to intermediate-spin state is possible in the electronic state change of FeTiO₃.