An In-Situ Raman Spectroscopic Study of the Phase Transition of Anhydrite under High Pressures
XIONG Xin1, 2, YUAN Xue-yin2*
1. School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China
2. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
Abstract：Anhydriteis one of the most widely distributed sulfite on the earth. Inorder to investigate the phase transition pressure and transformation mechanism between anhydrite and high pressure anhydrite, and to constrain the p-T area where the anhydrite Raman pressure sensor is applicable, in this paper the phase transition between anhydrite and high pressure anhydrite and the Raman spectra of both polymorphs were investigated by using a hydrothermal diamond anvil cell and laser Raman spectroscopy. Our results showed that the phase transition from anhydrite to a high pressure monazite structure occurred at pressures around 2.3 GPa, and that the phase transition pressure varied during the compressing and decompressing processes, which suggested the transformation between anhydrite and high pressure anhydrite was reconstructive process with significant hysteresis. As reconstructive transformations were controlled not only by pressure and temperature, but also by kinetics and metastability of the structure, hence explaining the discrepancy among the phase transition pressures between anhydrite and high pressure anhydrite. In contrast to those of anhydrite, the Raman vibrations of high pressure anhydrite were characterized by shifting of the ν1 mode from 1 128.28 to 1 024.39 cm-1, and by splitting of the ν2 mode into 441, 459 and 494 cm-1, ν3 into 1 136, 1 148, 1 158 and 1 173 cm-1, and ν4 into 598, 616, 646 and 671 cm-1, which ca be used as identifications for the transformation from anhydrite to high pressure anhydrite. The splitting of the ν2～ν4 vibrations into more bands indicated that the SO4 vibrations in high pressure anhydrite were affected by more nearby atoms, which was consistent with the high pressure anhydrite crystal symmetry (monoclinic) being lower than that of anhydrite (orthorhombic). Within the stability pressure range of anhydrite, All observed Raman bands of the SO4 vibrations, except for the ν2, 416, shifted to higher frequencies with constant ∂ν/∂p rates, mean while the Raman peak intensities and shapes remained stable, which meant that the Raman peak fitting and pressure calibration results could be equally precise under different pressures. In addition, we also verified the reliability of the anhydrite Raman pressure sensor by measuring the shifting rate of the ν1, 1 085 Raman peak position of calcite with pressure, and the phase transition pressures from calcite to CaCO3-Ⅱ and from CaCO3-Ⅱ to CaCO3-Ⅲ.
Key words：Anhydrite; Raman spectroscopy; Phase transition; High pressure
熊 欣，袁学银. 常温高压条件下硬石膏相变的原位拉曼光谱研究[J]. 光谱学与光谱分析, 2019, 39(04): 1075-1079.
XIONG Xin, YUAN Xue-yin. An In-Situ Raman Spectroscopic Study of the Phase Transition of Anhydrite under High Pressures. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(04): 1075-1079.
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