Crystal structure refinement of mantle minerals under high pressure and temperature using Rietveld method

对几种矿物进行了加压原位X射线衍射测量，并利用Rietveld结构精修方法对所得粉末衍射图谱进行了分析。高压是由金刚石对顶砧产生的，X射线衍射实验主要是在同步辐射装置PF和SPring 8上进行的。氢氧键距离的缩短控制了某些含水矿物（如KHCO_3和NaHCO_3）的压缩。KHCO_3在2.8Gpa左右发生相变。有趣的是，在9 Gpa下NaHCO_3中的氢键O-O距离达到2.4A ^^○，这表明氢键对称化的可能性。针铁矿的压缩行为与冰的压缩行为相似。激光退火对缓解材料的非静水压应变也有一定的作用。本文将激光退火应用于NiTiO_3-SiO_2的压缩实验。退火处理后的衍射图谱得到了很大的改善，Rietveld分析可以成功地进行，激光加热是在地球上创造下地幔条件的有力方法。我们在SPng 8的高压和高温条件下进行了原位X射线衍射实验，以澄清磁铁矿和铁之间反应的可能性。在2000℃和1000℃、40 Gpa下没有观察到反应的迹象。在20 Gpa和1500-1600 K下观察到CaSiO_3钙钛矿的衍射花样。用X射线衍射法测定了CaO的物态方程，讨论了CaSiO_3钙钛矿在下地幔最下部发生离解反应的可能性。

In-situ X-ray diffraction measurements under pressure were performed on several minerals and obtained powder diffraction patterns were analyzed by means of Rietveld structure refinement method. High pressure is generated by a diamond anvil cell (DAC) and X-ray diffraction experiments were mainly performed in synchrotron radiation facilities, such as PF and SPring8.Shortening of hydrogen bonded oxygen-oxygen distances controls compression of some hydrous minerals, such as KHCO_3 and NaHCO_3. A phase transition occurs on KHCO_3 at about 2.8 Gpa. It is interesting thai hydrogen bonded O-O distance in NaHCO_3 reaches to 2.4 A^^○ at 9 Gpa and this suggests a possibility of hydrogen bond symmetrization. Shortening of hydrogen bonded O-O distance also controls compression behavior of goethite and its shortening behavior is quite similar to that of ice VII.Laser annealing is quile useful for relaxing strain in materials caused by nonhydrostatic pressure Laser annealing was applied to compression experiments of NiTiO_3-ilmenite in PF. Obtained diffraction patterns after annealing treatment were greatly improved and Rietveld analysis could be done successfully up to 20 Gpa.Laser heating is a powerful method for creating lower mantle conditions on the earth. We performed insitu X-ray diffraction experiments under high pressure and temperature conditions at SPnng8 to clarify a possibility of a reaction between maguesite and iron. No evidence of the reaction was observed at 2000℃ and 1000℃ at 40 Gpa Diffraction patterns of CaSiO_3 perovskite could be observed at 20 Gpa and 1500-1600 K. Technical improvements are still needed but quite good quality diffraction patterns were recorded.EOS of CaO was determined by X-ray diffraction measurements using a hydraulically operated DAC and discusses a possibility of dissociation reaction of CaSiO_3 perovskile at the lowest part of the lower mantle.