Raman Spectroscopy Under Simultaneous High Pressure - High Temperature in a Laser Heated Diamond Cell: Thermal Pressure, Heat Capacity, Entropy, Thermal Expansivity, and Anharmonic

拟议的工作包括测量矿物在不同压力和温度条件下的振动模式，这使得可以通过统计方法或振动建模来对这种矿物进行热力学表征。到目前为止，使用振动建模获得的有用信息包括热容、熵、热膨胀系数和声速的压力导数。一个尚未得到充分利用的重要结果是：给定P和T时的热压可通过Pth=gEvib/V内能的振动模型得到。因此，在高压和温度同时进行的振动研究允许计算状态方程，这将支持对矿物热状态方程的许多X射线衍射研究。振动建模还将有助于提供一种超出所有热力学性质测量范围的外推方法。本课程将探讨磁性和电子对含铁矿物(或任何其他过渡金属矿物)的热容和熵的贡献。拟议的实验室工作包括在激光加热的金刚石顶压室中发展拉曼光谱。这些努力将集中在振动光谱和关键地幔阶段的状态方程之间的关联，但也将包括其他关键的热弹性参数。需要一种小型的单色仪系统，用于现场温度测量。我们建议扩展我们在威斯康星大学实验室目前的拉曼光谱能力，以允许在金刚石顶锤单元中使用二氧化碳激光加热来同时进行高温和压力。一旦仪器就位，将研究由X射线衍射确定其热状态方程的具有地球物理意义的重要矿物，包括镁硅钙钛矿和镁橄榄石及其高压多晶型以及其他镁硅相。除了在高压和高温下同时获得拉曼的第一级目标外，在钻石顶锤单元中的原位激光加热还将提供其他有用的数据：适当的相边界将在现场确定，任何不可熄灭的相都可以被检测到，并根据拉曼光谱模式识别可能的结构或空间群。体积是在许多地球内部的温度、成分和动力学模型中衡量许多其他性质的参数。对于地球物理、地球动力学、矿物学、岩石学以及凝聚态物理等许多分支的地球科学和物理工作者来说，所有深源条件下的V(P，T)以及压力下的热容和熵将是无价的。国际和平研究所已经接待了六名本科生研究人员，其中包括两名女性，参与实验室的研究。PIS目前的研究生是一名美洲原住民女性，是极少数在任何领域获得博士学位的人之一。

The proposed work consists of the measurement of vibrational modes of minerals at various pressure and temperature conditions, which allows thermodynamic characterization of this mineral through statistical methods or vibrational modeling. Useful information obtained so far using vibrational modeling includes the pressure derivatives of heat capacities, entropies, thermal expansivities, and sound velocities. One important result has not yet been fully exploited: Thermal pressure at a given P and T may be derived using vibrational modeling of internal energy, from PTH = gEvib/V. Thus, vibrational studies at simultaneous high pressure and temperature allow computation of the equation of state, which will support the many x-ray diffraction studies of the thermal equation of state of minerals. Vibrational modeling will also help provide a means for extrapolation beyond the range of the measurements of all thermodynamic properties. Magnetic and electronic contributions to heat capacity and entropy for iron-bearing minerals (or any others with transition metals) will be explored. The proposed laboratory work consists of the development of Raman spectroscopy in the laser heated diamond anvil cell. The efforts will concentrate on the correlation between vibrational spectra and the equations of state of key mantle phases, but will also include the other key thermoelastic parameters. A small, single monochromator system for in situ measurements of temperature is requested. We propose to extend the current Raman spectroscopic capabilities in our laboratory at UW to allow simultaneous high temperatures and pressures using CO2 laser heating in the diamond anvil cell. Once the instrument is in place, geophysically important minerals whose thermal equations of states have been determined by x-ray diffraction will be studied, including MgSi perovskite and forsterite and its high pressure poly-morphs as well as the other MgSiO3 phases. In addition to the first-order goal of obtaining Raman at simultaneous high pressures and temperatures, in situ laser heating in the diamond anvil cell will provide other useful data: phase boundaries where appropriate will be determined in situ and any unquenchable phases can be detected, with probable structures or space groups identified based on Raman spectral patterns.Volume is the parameter against which many other properties are scaled in many temperature, compositional and dynamical models of the Earth's interior. V(P,T) at all deep Earch conditions as well as heat capacity and entropy at pressure will be invaluable to workers in many branches of geoscience and physics, including geophysics, geodynamics, mineralogy, and petrology as well as condensed matter physics. The PI has hosted six of undergraduate researchers, including two women, to participate in research in the laboratory. The PIs current graduate student is a Native American woman, one of the very few to obtain a Ph.D. in any field.