Spin transition in germanate perovskite and post-perovskite at high pressure

地球表面的地质活动可以深刻地影响人类社会。它最终产生于行星内部深处正在进行的过程。这些大规模的过程反过来又受地球深部矿物成分的性质控制。 矿物的晶体和电子结构是其最基本的特征，所有其他物理和化学性质都是由此而来的。由于地幔的高压（数百万个大气压）和高温（数千度），人们对地幔底部附近矿物的晶体和电子结构的了解有限。该区域主要由硅酸盐矿物组成，其结构被称为钙钛矿和后钙钛矿。在这个项目中，研究人员将对这些结构进行实验室实验，以探索铁的掺入如何影响它们的特性。他将研究锗酸镁，这是一类与地球深部硅酸盐矿物相似的化合物，但可以在实验室中更容易达到的压力和温度下进行研究。通过这项工作，他将提供解释地球物理观测和约束地球内部物理过程所需的矿物性质的基本知识。该项目将对地幔热对流的理解产生影响，地幔热对流驱动了人类社会众多危害的起源板块构造，并提供了关于极端压力和温度条件对材料性能影响的见解。该项目还将为研究生的培训提供支持铁影响下地幔矿物的关键物理特性，包括密度，弹性，元素分配以及电导率和热导率。这些特性反过来又会影响地震和其他地球物理观测的解释，并限制地球深部的模型。钙钛矿和后钙钛矿是下地幔的主要结构。这些材料中的铁可以采用不同的价态和自旋状态，并且可以占据不同的结构位置。高压同步穆斯堡尔谱和X射线发射谱是研究地幔矿物中铁电子状态的主要工具。在这项研究中，研究人员将使用这些技术与传统的穆斯堡尔光谱一起探索钙钛矿和后钙钛矿在一系列压力和铁铝含量下的性质。他将使用镁锗酸盐类似物，与地球的硅酸盐相比，它的形成压力较低，这将允许研究压力对后钙钛矿性质的影响。预期的结果将提供强有力的约束的位置占位，价态和自旋状态的钙钛矿和后钙钛矿，以及最近的理论计算的直接测试。它们将有助于揭示铁在钙钛矿和后钙钛矿中的作用，这对于明确解释穆斯堡尔谱至关重要。他们还将使更全面地了解主要下地幔矿物的自旋配对行为，从而更好地约束地球深部地幔的属性。该奖项反映了NSF的法定使命，并已被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

The geological activity at Earth's surface can profoundly affect human societies. It ultimately arises from on-going processes within the planet deep interior. These large-scale processes are in turn controlled by the properties of the constituent minerals of the deep Earth. A mineral's crystal and electronic structures are its most fundamental characteristics, from which all other physical and chemical properties follow. Due to the high pressures (millions of atmospheres) and temperatures (thousands of degrees) of the Earth's mantle, there is limited knowledge of the crystal and electronic structures of minerals residing near its base. This region is primarily composed of silicate minerals that adopt structures known as perovskite and post-perovskite. In this project, the investigator will conduct laboratory experiments on these structures to probe how incorporation of iron affects their properties. He will study magnesium germanates, a class of compounds that are close analogs for the silicate minerals of the deep Earth yet can be studied at pressures and temperatures that are more easily attainable in the laboratory. Through this work, he will provide fundamental knowledge of mineral properties that are needed to interpret geophysical observations and constrain the physical processes in Earth's interior. This project will have implications for the understanding of mantle thermal convection, which drives plate tectonics at the origin of numerous hazards for human societies, and provide insights on the effect of extreme conditions of pressure and temperature on materials properties. The project will also provide support for the training of a graduate studentIron influences key physical properties of lower mantle minerals including density, elasticity, element partitioning, and electrical and thermal conductivity. These properties in turn affect the interpretation of seismic and other geophysical observations and constrain models of the deep Earth. Perovskites and post-perovskites are major structures of the lower mantle. Iron in these materials may adopt different valences and spin states and may occupy different structural sites. High-pressure synchrotron Mossbauer spectroscopy and X-ray emission spectroscopy are the primary tools for investigating the electronic state of iron in mantle minerals. In this study the investigator will use these techniques together with conventional Mossbauer spectroscopy to explore the properties of perovskites and post-perovskites over a range of pressures and iron and aluminum contents. He will use magnesium gemanate analogs which lower pressure of formation, compared to that of Earth's silicates, will allow investigating the effect of pressure on post-perovskite properties. The expected results will provide strong constraints on the site occupancies, valences and spin states of perovskite and post-perovskite, as well as a direct test of recent theoretical calculations. They will contribute to unveiling the role of iron in perovskite and post-perovskite which is crucial for the unambiguous interpretation of Mossbauer spectra. They will also enable a more comprehensive understanding of spin-pairing behavior in major lower mantle minerals, thus better constraining the properties of Earth's deep mantle.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.