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

该提案计划重点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：白云石，选定的氧化物尖晶石，如镁铁（MgFe 2 O 4）和镁铁尖晶石（Mg 2 TiO 4），以及斜方辉石（opx，En 50 Fs 50）。目标是使用Rietveld精化确定这些材料中的有序状态作为温度和压力的函数，确认由Luth从他对白云石的淬火实验中提出的击穿曲线，并确定在高PT下有序度（X）与P波和S波速度之间的关系。人们认识到，淬火实验后，单晶结构的测定可能是有用的，在高压或高温单独的测量是有价值的。然而，现在有机会将晶体学测量与第一次同时保持高压和高温的超声波旅行时间的估计结合起来，从而更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及其对稳定性和弹性的影响的问题。X射线衍射提供了X和热EoS的记录，而新的超声工作设置提供了P和S波速度的同时测定。后者的测量是至关重要的，因为不再需要改变样品来进行P波和S波的单独测量;几个小组报告说，虽然在某些材料（例如斜方辉石）中，P波似乎不受阳离子取代的影响，但S波速度确实会变化。一些技术的发展将伴随着该项目，并希望这将发现在其他团体的研究中的应用感兴趣的同时实时测定结构和弹性，并在相关的原子结构与物理性质。

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.