Anisotropic electrical conductivity changes in FeTiO3 structure transition under high pressure

IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Physics and Chemistry of Minerals Pub Date : 2024-02-05 DOI:10.1007/s00269-023-01261-6
Takamitsu Yamanaka, Yuki Nakamoto, Masafumi Sakata, Katsuya Shimizu, Takanori Hattori
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Abstract

Electrical resistivity measurements on oriented FeTiO3 ilmenite using single crystals at high pressures proves that FeTiO3 ilmenite shows anisotropic electrical resistivity. The resistivity in the direction perpendicular to the c-axis decreased monotonously with increasing pressure. In contrast, the resistivity in the parallel direction to the c-axis initially decreased and slightly increased with increasing pressure above 6 GPa. It then resumed decreasing above 8 GPa. The hallow-shape of the curvature was observed. Neutron and synchrotron X-ray diffraction experiments provided an accurate picture of the pressure-induced changes of the FeTiO3 ilmenite structure. FeTiO3 transforms neither into perovskite nor LiNbO3 phase under pressures up to 28 GPa. However, different compression curves were observed for both FeO6 and TiO6 octahedra below 8 GPa. FeO6 is more compressible and flexible than TiO6. Among Fe–Fe, Ti–Ti and Fe–Ti interatomic distances, the shortest Fe–Ti distance presents the highest electrical restivity and electron mobility according to Fe2+Ti4+ and Fe3+Ti3+ by electron super-exchange mechanism, which is enhanced during compression. At high pressure, the electron configuration of Fe2+ (3d6) is more strongly changed than Ti4+ (3d0) and the former cation is the emphasized by Jahn–Teller effect in the ligand field of C3v molecular symmetry. The anisotropic electrical resistivity and non-uniform structure change of Fe–Ti interatomic distance can be explained by possible spin transition. The spin transition of Fe from high-spin to intermediate-spin state is possible in the electronic state change of FeTiO3.

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高压下 FeTiO_3 结构转变中各向异性的导电率变化
在高压下使用单晶体对取向氧化铁钛锰矿进行的电阻率测量证明,氧化铁钛锰矿具有各向异性的电阻率。垂直于 c 轴方向的电阻率随着压力的增加而单调下降。与此相反,与 c 轴平行方向的电阻率在 6 GPa 以上随着压力的增加最初下降,然后略有上升。然后在 8 GPa 以上恢复下降。观察到了曲率的霍洛形状。中子和同步辐射 X 射线衍射实验为铁钛锰矿结构在压力作用下的变化提供了准确的图像。在高达 28 GPa 的压力下,FeTiO3 既不会转变为透辉石相,也不会转变为铌酸锂相。然而,在 8 GPa 以下,FeO6 和 TiO6 八面体的压缩曲线有所不同。与 TiO6 相比,FeO6 的可压缩性和柔韧性更高。在Fe-Fe、Ti-Ti和Fe-Ti原子间距离中,Fe-Ti距离最短的Fe2+Ti4+和Fe3+Ti3+通过电子超交换机制表现出最高的电静电性和电子迁移率,这种电静电性和电子迁移率在压缩过程中得到增强。在高压下,Fe2+(3d6)的电子构型比 Ti4+(3d0)发生了更强烈的变化,在 C3v 分子对称性的配位场中,前者阳离子受到 Jahn-Teller 效应的强调。各向异性的电阻率和 Fe-Ti 原子间距离的非均匀结构变化可以用可能的自旋转变来解释。在 FeTiO3 的电子状态变化中,FeKβ 有可能从高自旋态转变为中自旋态。
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来源期刊
Physics and Chemistry of Minerals
Physics and Chemistry of Minerals 地学-材料科学:综合
CiteScore
2.90
自引率
14.30%
发文量
43
审稿时长
3 months
期刊介绍: Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)
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