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Raman and infrared spectra to monitor the phase transition of natural kyanite under static compression
Journal of Raman Spectroscopy ( IF 2.4 ) Pub Date : 2020-07-27 , DOI: 10.1002/jrs.5954
Jing Gao 1 , Wanghua Wu 2 , Lihui Jia 1 , Ching‐Pao Wang 3 , Yingxin Liu 4 , Chaowen Xu 5 , Fei Chen 1 , Chenhui Fei 1 , Wen Su 1
Affiliation  

The stability of kyanite Al2SiO5 at high pressure is of significance in understanding the fate of the subducted crust and how they recycle within the Earth. Thus, in situ high‐pressure vibrational spectra of natural kyanite are presented. The shift amplitudes of the measured modes dependent on pressure manifest the contraction of the AlO bond bears the most compression of kyanite. At 9.7 GPa, a first‐order phase transition to kyanite‐II occurs, which is distinguished by changes occurred in the entire spectral region, including the pressure dependences of the modes, the wavenumber jumps of some peaks, the splitting of a SiO symmetric stretching band, and the emergence of new modes. A Raman mapping image is collected illustrating kyanite and kyanite‐II in coexistence at 10.0 GPa. Emphasize that, as is revealed by the infrared spectra, a part of HO···O distance becomes elongated after the transformation. At higher pressure up to 18.6 GPa, the Raman spectra disclose little effects associated with further transformations. Finally, releasing pressure to ambient leads to recovery of pure kyanite. Our results mark a lowest pressure limit of the change in the intermolecular and intramolecular bonding of kyanite and shed new lights on the crystal chemistry of aluminosilicate under mantle pressures.

中文翻译:

拉曼光谱和红外光谱可监测天然蓝晶石在静态压缩下的相变

蓝晶石Al 2 SiO 5在高压下的稳定性对于理解俯冲壳的命运以及它们如何在地球内循环是至关重要的。因此,提出了天然蓝晶石的原位高压振动光谱。测得的模态随压力的变化幅度表明,Al bondO键的收缩具有最大的蓝晶石压缩率。在9.7 GPa时,发生向蓝晶石II的一阶相变,其特征是在整个光谱区域中发生了变化,包括模式的压力依赖性,某些峰的波数跳跃,Si split的分裂。O对称的伸缩带,并出现了新的模式。收集了一个拉曼映射图像,显示了10.0 GPa下的蓝晶石和蓝晶石II共存。要强调的是,如红外光谱所揭示的,变换后部分HO ···O距离变长了。在高达18.6 GPa的更高压力下,拉曼光谱显示出与进一步转化相关的影响很小。最后,释放压力到环境导致回收纯蓝晶石。我们的结果标志着蓝晶石分子间和分子内键合变化的最低压力极限,并为地幔压力下硅铝酸盐的晶体化学提供了新的思路。
更新日期:2020-07-27
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