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Local structures and electoric conduction mechanism of minerals in Earth's lower mantle.

地球下地幔矿物的局部结构和导电机制。

基本信息

批准号：
11640479
负责人：
YOSHIASA Akira
金额：
$ 0.26万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

(Mg, Fe, Al)(Si, Al) O3 perovskite and (Mg, Fe) O magnesio-wustite are believe to major components of the Earth's lower mantle. It is well known that the Earth's lower mantle exhibits high electric conductivity (1-10 S/m). The knowledge of the local structure is of primary importance for the understanding of the complicated physical properties. An anharmonic effective pair potential can be investigated using the EXAFS technique. The anharmonicity in potentials is directory correlated with physical properties such as the thermal expansion, thermal conductivity and ionic conductivity. We have precisely reinvestigated the conductivity and conduction mechanism of single crystals of such lower mantle minerals and analogues.Single crystals of the Earth's internal materials were grown by various methods under high-pressure and high -temperature (e.g. 25 GPa, 2000 K and 0.1 MPa, 3000 K). Conductivity was measured by a complex impedance method under various conditions and atmospheres. Precise c … More rystal structure and thermal properties for many materials in the Earth's mantle such as majorite garnet, magnesio -wustite, MgSiO3 perovskite solid -solution and stishovite have been revealed by EXAFS spectroscopy and diffraction method.The probability of finding mobile ions at potential barrier was estimated under high temperature and high pressure by EXAFS spectroscopy. The probability of finding mobile ions at potential barrier is larger than several percent in superionic conducting minerals at the highest temperature. Conductivities of analogues of MgSiO3 perovskite solid-solution were measured and showing that the perovskite type compound became solid electrolytes with ionic conduction near their melting points. It was clarified that activation energies for intrinsic conduction of perovskite type compounds are about 2.0 eV.The value indicates the summation of the vacancy formation energy and the vacancy migration energy, where the vacancy formation energy is about 1.0 eV.In this study, it was revealed that the high conductivity in Earth's lower mantle cannot explained by the intrinsic conduction mechanism of perovskite crystals. Possible mechanism in the lower mantle is considered as extrinsic ionic conduction of (Mg, Fe, Al)(Si, Al) O3 perovskite with eutectic reactions or as a conduction of (Mg, Fe) O magnesio-wustite by a large polaron. Less

(Mg, Fe, Al)(Si, Al) O3 钙钛矿和(Mg, Fe) O 镁方铁矿被认为是地球下地幔的主要成分。众所周知，地球下地幔具有高电导率（1-10 S/m）。局部结构的知识对于理解复杂的物理性质至关重要。可以使用 EXAFS 技术研究非谐波有效对电势。电势的非谐性与热膨胀、热导率和离子电导率等物理性质直接相关。我们精确地重新研究了此类下地幔矿物及其类似物的单晶的电导率和传导机制。地球内部材料的单晶是在高压和高温（例如25 GPa，2000 K和0.1 MPa，3000 K）下通过各种方法生长的。在各种条件和气氛下通过复阻抗法测量电导率。通过EXAFS光谱和衍射方法，揭示了地幔中许多物质的精确晶体结构和热性质，如多数石榴石、镁方铁矿、MgSiO3钙钛矿固溶体和石英石。通过EXAFS光谱估算了高温高压下在势垒处发现移动离子的概率。在最高温度下，在超离子导电矿物中，在势垒处找到移动离子的概率大于几个百分点。测量了 MgSiO3 钙钛矿固溶体类似物的电导率，结果表明钙钛矿型化合物在熔点附近成为具有离子传导性的固体电解质。阐明了钙钛矿型化合物本征导电的活化能约为2.0 eV。该值表示空位形成能和空位迁移能的总和，其中空位形成能约为1.0 eV。这项研究揭示了地球下地幔的高电导率不能用钙钛矿晶体的本征导电机制来解释。下地幔中可能的机制被认为是 (Mg, Fe, Al)(Si, Al) O3 钙钛矿与共晶反应的外在离子传导，或者是 (Mg, Fe) O 镁方铁矿通过大极化子的传导。较少的