In-Situ Study of Pressure Effect on Cation Order-Disorder Phenomenon in Mantle Minerals

有序-无序现象在矿物的能量学和晶体化学中起着关键作用。矿物中阳离子有序无序分布的变化会导致其自由能的变化，从而导致相稳定性和物理性质的变化，如强度、弹性模量和导热系数。本文的目的是研究地幔矿物在高压高温下的阳离子有序无序现象，以便准确地了解地球内部矿物的物理性质。该项目将利用最新发展的最先进的原位x射线衍射系统，该系统具有多砧大容量压力机和单色同步辐射，位于NSLS的X17B光束线上。基于原位衍射数据的晶体结构细化是主要的分析工具。待研究的矿物包括橄榄石、瓦德利石、正辉石和尖晶石。在这一建议中，我们重点研究了这些矿物中Fe（或Ni）和Mg（或Al）阳离子之间的有序-无序分布。这些研究将显著改善地幔条件下矿物物理性质的详细信息，提高地幔建模关键物理参数的准确性。

Chen and WeidnerEAR-9909413Order-disorder phenomena play a key role in the energetics and crystal chemistry of minerals. Variation of the cation order-disorder distribution in minerals results in changes in their free energy, and, therefore phase stability and physical properties, such as strength, elastic moduli, and thermal conductivity. The goal of this proposal is to study the cation order-disorder phenomena in mantle minerals at high pressure and temperature in order to understand accurately the physical properties of the minerals in the Earth interior. The project will take advantage of new developments of the state-of-art in-situ x-ray diffraction system with a multi-anvil large volume press and monochromatic synchrotron radiation at the X17B beamline of the NSLS. Crystal structure refinement based on the in-situ diffraction data is the major analytical tool. The minerals to be studied include olivine, wadsleyite, orthopyroxene and spinel. In this proposal we focus on the order-disorder distribution between Fe (or Ni) and Mg (or Al) cations in these minerals. The proposed studies will significantly improve the detail in information of the physical properties of the minerals at the mantle conditions and increase the accuracy of critical physical parameters for mantle modeling.