Crystal Structures of Minerals at Ultrahigh Pressures and Temperatures

现代地球物理学的一个基本目标是了解行星的结构以及它们如何随着地质时间的推移而演变。这需要详细了解地球内部不同区域的组成和矿物学，并确定一些重要的化学和物理性质，如可压缩性、熔融温度和流变学。然而，地球和行星的内部几乎完全隐藏在直接观察之外。因此，有必要通过地球物理观测，如从地震中推断出的地震波速随深度的变化，以及通过实验室实验来推断地球深部的性质。后者具有挑战性，因为地球深层的压力大约是地球表面压力的100万倍，温度可高达5000 K。激光加热的钻石压腔是唯一可以再现地幔和地核深处压力-温度条件的实验室技术。在这个项目中，我们将使用这个装置和先进光子源的同步辐射设备来研究一些与深部地幔和地核相关的基本材料的性质。对于铁、钼和铁硫化物，我们将在高达250 Gpa和4000 K的条件下进行原位X射线衍射实验。这些结果将为潜在核心材料的物相和状态方程提供新的约束，并将有助于解释冲击压缩和静态熔融数据。最近在接近地球核-地幔边界的条件下发现了一个后钙钛矿相，这对理解这一区域的结构和动力学具有重大意义。我们还将对(Mg，Fe)GeO_3-Al_2O_3模拟系统中的钙钛矿相和后钙钛矿相进行全面的研究。我们将考察组成变量(Fe，Al)对该系统中钙钛矿和后钙钛矿晶型的状态方程、转变压力和结构响应的影响。最后，我们将研究超高压下的二氧化硅，以检验二氧化硅中进一步相变的理论预测。这一研究计划将通过向研究生和本科生提供高压科学、同步辐射X射线技术、矿物物理和全球地球物理方面的高级培训，来加强研究和教育基础设施。我们的研究将提供有关高压和高温下的材料物理以及行星内部结构和状态的基本新知识。

A fundamental goal of modern geophysics is to understand the structure of planets and how they have evolved over geological time. This requires a detailed knowledge of the composition and mineralogy of different regions of the Earth's interior coupled with determination of some important chemical and physical properties such as compressibility, melting temperature, and rheology. However, the interiors of the Earth and planets are almost completely hidden from direct observation. As a result, it is necessary to infer properties of the deep Earth from geophysical observations, such as the variation of seismic wave velocity with depth inferred from earthquakes, and through laboratory experimentation. The latter is challenging as the Earth's deep interior is at pressures approximately one million times greater than that at Earth's surfaces and temperatures can reach up to 5000 K. The laser-heated diamond anvil cell is the only laboratory technique that can reproduce the pressure-temperature conditions in the deep mantle and core of the Earth. In this project, we will use this device in combination with synchrotron radiation facilities at the Advanced Photon Source to study the properties of a number of fundamental materials relevant to the deep mantle and core.For iron, molybdenum, and iron sulfide, we will carry out in situ x-ray diffraction experiments to conditions as high as 250 GPa and 4000 K. These results will provide new constraints on phases and equation of state of potential core materials, and will also aid in the interpretation of shock compression and static melting data. The recent discovery of a post-perovskite phase at conditions approaching the Earth's core-mantle boundary has major implications for understanding the structure and dynamics of this region. We will also carry out a comprehensive study of perovskite and post-perovskite phases in the analog system (Mg,Fe)GeO3-Al2O3 to 120 GPa and 2500 K. We will examine how compositional variables (Fe, Al) affect the equation of state, transition pressures, and structural response of both the perovskite and post-perovskite polymorphs in this system. Finally, we will examine SiO2 at ultrahigh pressures to test theoretical predictions of further phase transitions in silica. This research program will enhance research and education infrastructure by providing advanced training in high-pressure science, synchrotron x-ray techniques, mineral physics and global geophysics to graduate and undergraduate students. Our research will provide fundamental new knowledge about the physics of materials at high pressures and temperatures and the structure and state of planetary interiors