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。它最终产生于地球深处正在进行的过程。这些大规模的过程反过来又受到地球深处组成矿物的性质的控制。矿物的晶体和电子结构是其最基本的特征，所有其他的物理和化学性质都是由此而来。由于地幔的高压（数百万个大气压）和温度（数千度），人们对其底部附近矿物的晶体和电子结构的了解有限。该地区主要由硅酸盐矿物组成，采用钙钛矿和后钙钛矿的结构。在这个项目中，研究者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性能。他将研究锗酸镁，这是一种类似于地球深处硅酸盐矿物的化合物，但可以在实验室更容易获得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限制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，地幔热对流驱动板块构造，是人类社会众多危害的起源，并提供对极端压力和温度条件对材料特性的影响的见解。该项目还将为培训一名研究生提供支持。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、电导率和导热性。这些性质反过来影响地震和其他地球物理观测的解释，并限制了地球深部的模型。钙钛矿和后钙钛矿是下地幔的主要构造。这些材料中的铁可能采用不同的价态和自旋态，并可能占据不同的结构位点。高压同步穆斯堡尔能谱和x射线发射能谱是研究地幔矿物中铁电子态的主要工具。在这项研究中，研究者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和铝含量下的性质。他将使用镁衍生物，与地球上的硅酸盐相比，它的形成压力更低，从而可以研究压力对钙钛矿后性质的影响。预期的结果将对钙钛矿和后钙钛矿的占位、价和自旋态提供强有力的约束，并对最近的理论计算进行直接测试。他们将有助于揭示铁在钙钛矿和后钙钛矿中的作用，这对穆斯堡尔光谱的明确解释至关重要。它们还将使我们能够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性质。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.