Anharmonicity and Phase Transitions of Mantle Phases Using Simultaneous High Pressure-High Temperature Raman Spectroscopy in the Laser Heated Diamond Cell

ChopelasEAR-0106120同时在高压和高温下测量振动模式为扩大地球物理中拉曼光谱的技术水平提供了许多重要机会。首先，可以在现场快速确定相边界。其次，可以很容易地检测到新的不可熄灭的相，并根据光谱模式识别可能的结构或空间群。第三，这些实验直接测量本征非谐性，这是用Mie-Gruneisen状态方程外推重要参数所需的值，如从1大气压到地球深处的热膨胀系数，或使用Mie-Gruneisen状态方程计算材料在P-T空间的密度。地球温度、成分和动力学模型通常依赖于对候选矿物的这些性质的推断，以适应地球深处的条件。我们目前的能力包括与美因茨实验室几乎相同的实验安排：带有CCD摄像机和光电倍增管的拉曼双单色仪、钻石电池和激发激光。美因茨实验室使用二氧化碳激光器加热的初步数据表明，这种方法是可行的。在这份建议书中，要求使用二氧化碳激光器。我们建议将我们在UNLV的实验室目前的拉曼光谱能力扩展到同时使用高温和高压，使用金刚石顶压室中的二氧化碳激光加热。一旦实验室升级，研究将首先集中在两种具有重要地球物理意义的矿物镁橄榄石和镁硅酸盐钙钛矿上，这两种矿物都是重要的地幔相。以前对这些在高温或高压下的拉曼研究可以用来进行比较。第一个结果将集中于使用麦克斯韦关系对Mie Gruneisen状态方程和地幔条件下的热膨胀率提供直接约束。

ChopelasEAR-0106120Measurement of vibrational modes at simultaneous high pressures and temperatures offers many important opportunities to expand the state of the art in Raman spectroscopy in geophysics. First, phase boundaries can be quickly determined in situ. Second, new unquenchable phases can be easily detected, with probable structures or space groups identified based on spectral patterns. Third, these experiments directly measure the intrinsic anharmonicity, a value required for extrapolating important parameters such as thermal expansivity from 1 atm to deep earth conditions or calculating densities of a material in P-T space using the Mie-Gruneisen equation of state. Earth temperature, compositional, and dynamical models generally rely on extrapolation of these properties of candidate minerals to deep Earth conditions.Our current capabilities include a nearly identical experimental arrangement as those in Mainz: Raman double monochromator with CCD camera and photomultiplier tube, diamond cells, and excitation laser. Preliminary data from the Mainz laboratory using a CO2 laser for heating show that this method is feasible. A CO2 laser is requested in this proposal. We propose to extend the current Raman spectroscopic capabilities in our laboratory at UNLV to simultaneous high temperatures and pressures using CO2 laser heating in the diamond anvil cell. Once the laboratory is upgraded, the study will first focus on the two geophysically important minerals forsterite and magnesium silicate perovskite, both important mantle phases. Prior Raman studies of these at either elevated temperatures or elevated pressures are available for comparison. First results will focus on providing direct constraints on the Mie Gruneisen equation of state and on thermal expansivity at mantle conditions using a Maxwell relation.