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Yamanaka, Takamitsu*; Hattori, Takanori
Physics and Chemistry of Minerals, 53(3), p.21_1 - 21_11, 2026/09
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Bulk modulus and electron density distribution of high-pressure polymorphs of Fe-Ti-O minerals (Fe
O
magnetite, Fe
TiO ulv
spinel, 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.
structure transition under high pressureYamanaka, Takamitsu*; Nakamoto, Yuki*; Sakata, Masafumi*; Shimizu, Katsuya*; Hattori, Takanori
Physics and Chemistry of Minerals, 51(1), p.4_1 - 4_10, 2024/02
Times Cited Count：4 Percentile：50.55(Materials Science, Multidisciplinary)Neutron and synchrotron X-ray diffraction and electric conductivity measurements of FeTiO ilmenite were performed under pressures. Ilmenite structure is retained up to 28 GPa. Structure analysis revealed that FeO
and TiO are compressible and less compressible below 8 GPa, respectively. The resistivity is lowest along the Fe-Ti direction that has shortest interatomic distance among all the metal ion pairs. The resistivity in the direction normal to c-axis monotonically decreases with pressure, whereas that along c-axis shows hallow-shape with pressure. Maximum entropy analysis shows that electron configuration of Fe
(3
) is more strongly changed than Ti
(3
) under compression. The anisotropic electrical conductivity and non-uniform structure change of Fe-Ti interatomic distance can be explained by the possible spin transition from high-spin state to intermediate-spin state of Fe cation.
Fe
O solid solutions under high-pressure and high-temperature conditionsYamanaka, Takamitsu*; Hirao, Naohisa*; Nakamoto, Yuki*; Mikouchi, Takashi*; Hattori, Takanori; Komatsu, Kazuki*; Mao, H.-K.*
Physics and Chemistry of Minerals, 49(10), p.41_1 - 41_14, 2022/10
Times Cited Count：5 Percentile：24.10(Materials Science, Multidisciplinary)Magnetic and crystal structure of MnFeO solid solutions under high-PT conditions are investigated by neutron diffraction and synchrotron M
ssbauer spectroscopy. The ferrimagnetic-paramagnetic transition and tetragonal-cubic transition of MnFeO spinel occur at 100
C and 180C, respectively, suggesting both the transitions are not coupled. The structure transition temperature decreases with pressure. Mssbauer experiments and neutron diffraction revealed that the Fe occupancy in tetrahedral site increases increase with pressure, suggesting MnFeO phase approaches inverse spinel. Magnetic structure refinement clarified paramagnetic and ferrimagnetic structure of MnFeO and MnFeO. These spinels transform into high-pressure orthorhombic phases at 18.4 and 14.0 GPa, respectively, indicating lower transition pressure with increasing Mn content.
FeO spinel and postspinel with elevating pressureYamanaka, Takamitsu*; Rahman, S.*; Nakamoto, Yuki*; Hattori, Takanori; Jang, B. G.*; Kim, D. Y.*; Mao, H.-K.*
Journal of Physics and Chemistry of Solids, 167, p.110721_1 - 110721_10, 2022/08
Times Cited Count：4 Percentile：20.12(Chemistry, Multidisciplinary)High-pressure neutron diffraction proved that MnFeO and MnFeO spinels transform into CaMnO-type structure above 18 GPa and 14 GPa, respectively. The transition pressure of MnFeO solutions decreases with increasing Mn content. Synchrotron X-ray Mssbauer experiments revealed that Fe and Fe
distribution at the tetrahedral (A) and octahedral (B) sites in the spinel structure changes with pressure. MnFeO and MnFeO spinels are ferrimagnetic and the CaMnO-type phase is paramagnetic. The temperature dependence of resistivity indicates that both spinels are semiconductors wherein electrons hop between cations at the A and B sites. A pressure-induced shortening of B-B distance promoted conduction via greater electron mobility between adjacent B cations. The Fe and Fe occupancies at the B sites in MnFeO are much larger than those in MnFeO. The CaMnO-type phase is metallic. Theoretical calculation confirmed the metallic character and Fe d-orbitals strongly renormalized compared to Mn d-orbitals.
