High Pressure-Temperature Equations of State, Oxygen Fugacity, and Earth's Core

材料在高温高压下的性质对于了解地球内部深处至关重要。该项目通过在高压、高温条件下（高达100 GPa和2500 K）原位测量晶胞体积，扩展了我们对几种重要材料的状态方程（压力-体积-温度关系）的理解。同时测量金属及其共存氧化物的压力-体积-温度比单独测量每个相提供了更精确的测量它们的相对状态方程。同步加速器X射线衍射用于测量两个相的体积，并且使用激光加热的金刚石砧单元产生高压和高温。使用多砧压机的补充研究也在进行中;这些研究加强了较低压力范围（25 GPa）的数据集。这两组实验的实验方法在早期的研究中得到了成功的证明，但没有得到广泛的应用。主要研究金属和氧化物，包括铁-铁氧化物、镍-镍氧化物和铁-镍氧化物。这些数据在地球内部的研究中有几个应用。一个是改进扩展的氧逸度缓冲高压，通过整合精确的，实验确定的相对体积共存的金属氧化物相。这些结果使人们能够更好地量化在高压下的氧势，这是需要了解的，例如，核幔相互作用和地幔中的元素分配。此外，许多高压地球化学研究的氧逸度条件要么由这些金属氧化物缓冲区控制，要么参考这些金属氧化物缓冲区。精确比较基于不同缓冲液的实验结果需要了解这些缓冲液随压力增加的相对变化。最后，这些研究有助于直接比较实验确定的候选核心成分的密度与观察到的，地震学约束的核心密度分布。这里需要更多的数据来提高精度和减少外推，特别是在高温下。从这个项目中获得的信息将有助于我们了解行星的化学演化和核心的形成。

The properties of materials at high pressure and temperature are essential for understanding the Earth's deep interior. This project is extending our understanding of the equations of state (pressure - volume - temperature relationships) of several geophysically important materials, through in situ measurement of unit cell volumes under high pressure, high temperature conditions (up to 100 GPa and 2500 K). Simultaneous pressure - volume - temperature measurements of a metal and its coexisting oxide provide a more precise measure of their relative equations of state than measurements of each phase separately. Synchrotron x-ray diffraction is used to measure volumes of both phases, and high pressures and temperatures are generated using a laser heated diamond anvil cell. Complementary studies using a multi-anvil press are also underway; these strengthen the data set in the lower pressure range ( 25 GPa). The experimental methodologies for both sets of experiments was successfully demonstrated in earlier investigations, but had not been broadly applied. Metals and oxides are being studied primarily, including iron-iron oxide, nickel-nickel oxide, and rhenium-rhenium oxide. There are several applications of these data to studies of the Earth's interior. One is the improved extension of oxygen fugacity buffers to high pressures, by integration of precise, experimentally determined relative volumes of coexisting metal-oxide phases. These results allow one to better quantify the oxygen potential at high pressures, which is needed to understand, for example, core-mantle interaction and elemental partitioning in the mantle. Furthermore, the oxygen fugacity conditions of many high pressure geochemical studies are either controlled by, or referenced to, these metal-oxide buffers. Precise comparison of experimental results that are based on different buffers requires knowledge of the relative shifts of those buffers with increasing pressure. Finally, these studies facilitate direct comparison of experimentally determined densities of candidate core constituents with the observed, seismologically constrained density profiles of the core. More data have been needed here to improve precision and reduce extrapolations, especially at high temperature. The information gained from this project will benefit our understanding of the chemical evolution of the planet and the formation of the core.