Experimental Tests of the Effects of Order-Disorder on Stability and Elasticity of Minerals at High Pressures and Temperatures

该提案计划集中研究与地球下地壳和地幔直接相关的三个系统，并且存在大量数据：白云岩，选定的氧化尖晶石，如镁铁素体（MgFe2O4）和qandilite (Mg2TiO4)，和正辉石（opx, En50Fs50）。目标是使用Rietveld精化来确定这些材料的有序状态作为温度和压力的函数，确认Luth从他的白云石淬火实验中提出的击穿曲线，并确定在高PT下有序(X)与P波和s波速度之间的关系。人们认识到，淬火实验之后的单晶结构测定是有用的，并且在高压或高温下单独测量是有价值的。然而，现在有机会将晶体学测量与同时保持高压和高温的超声波传播时间估计结合起来，从而更密切地接近与地球下地壳和上地幔直接相关的测量。这些同时测量非常适合于有序-无序问题及其对稳定性和弹性的影响。X射线衍射提供了X和热EoS的记录，而超声波工作的新设置提供了P波和s波速度的同时测定。后一种测量是至关重要的，因为不再需要改变样品来执行P波和s波的单独测量；几个小组报告说，虽然在某些材料中（例如正硅氧烷），纵波似乎不受阳离子取代的影响，但s波速度确实变化。一些技术发展将伴随该项目，希望这将在其他对同时实时确定结构和弹性以及将原子结构与物理性质相关联感兴趣的小组的研究中得到应用。

Parise and ChenEAR-0125094This proposal plans a focused study on three systems of direct relevance to the Earth's lower crust and mantle and for which considerable data exist: dolomite, selected oxide spinels such as magnesioferrite (MgFe2O4) and qandilite (Mg2TiO4), and orthopyroxene (opx, En50Fs50). The goal is to determine the state of order in these materials as a function of both temperature and pressure using Rietveld refinement, confirm the breakdown curve proposed by Luth from his quench experiments on dolomite, and determine the relationship between order (X) and P- and S-wave velocities at high PT. It is recognized that quench experiments followed by single crystal structure determination can be useful, and that measurements at high pressure or high temperature alone are valuable. However, an opportunity exists now to couple crystallographic measurements with the estimation of ultrasonic travel times at simultaneously maintained high pressure and temperature for the first time, and thereby more closely approach measurements directly relevant to the Earth's lower crust and upper-mantle. These simultaneous measurements are ideally suited to the problem of order-disorder and its effects on stability and elasticity. X-Ray diffraction provides a record of X and of the thermal EoS while the new set up for ultrasonic work provides simultaneous determinations of P and S-wave velocities. The latter measurements are crucial since there is no longer a need to change samples to perform separate measurements for P- and S-waves; several groups report that while in some materials (orthopyroxene for example) P-waves appear unaffected by cation substitution, the S-wave velocities do vary. Some technical development will accompany the project and it is hoped this will find application in the research of other groups interested in simultaneous real-time determination of structure and elasticity, and in correlating atomic structure with physical properties.