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

材料在高压和高温下的特性对于了解地球深处的内部是至关重要的。该项目通过在高压、高温条件下（高达100 GPa和2500 K）的原位测量，扩展了我们对几种地球物理学上重要材料的状态方程（压力-体积-温度关系）的理解。同时测量一种金属及其共存的氧化物的压力、体积和温度，比单独测量每一相的状态方程更精确。同步加速器x射线衍射用于测量两相的体积，并使用激光加热的金刚石砧细胞产生高压和高温。使用多砧压力机的补充研究也在进行中；这加强了较低压力范围（25gpa）的数据集。这两组实验的实验方法在早期的研究中都得到了成功的证明，但没有得到广泛的应用。主要研究的是金属和氧化物，包括铁-铁氧化物、镍-镍氧化物和铼-铼氧化物。这些数据在地球内部的研究中有几种应用。一个是通过整合精确的、实验确定的共存金属氧化物相的相对体积，改进了氧逸度缓冲液在高压下的扩展。这些结果使人们能够更好地量化高压下的氧势，这需要理解，例如，核-地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中的氧逸度条件要么由这些金属氧化物缓冲液控制，要么参考这些缓冲液。要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而发生的相对位移。最后，这些研究有助于将实验确定的候选岩心成分密度与观测到的地震约束岩心密度剖面进行直接比较。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地球的化学演化和地核的形成。

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.