常温高压条件下硬石膏相变的原位拉曼光谱研究
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摘要
硬石膏(CaSO_4)是地球上分布最广的硫酸盐矿物之一,为研究硬石膏向高压硬石膏转变的压力条件和相变机理、确定硬石膏拉曼光谱压标的适用范围,实验结合水热金刚石压腔和激光拉曼光谱实验技术,研究了常温高压条件下硬石膏的相变过程以及硬石膏和高压硬石膏的拉曼光谱特征。实验结果显示,常温条件下硬石膏向高压硬石膏发生相变的压力在2.3 GPa左右,但是该相变压力在增压和降压过程中存在较大差异,表明硬石膏与高压硬石膏的转变过程存在明显滞后性,证实了该相变过程属于重建型相变。由于重建型相变的控制因素除了温度和压力之外,还包括相变的速率以及矿物结构的亚稳定性等,从而很好地解释了不同实验者获得的硬石膏与高压硬石膏的相变压力之间存在的巨大差异。与硬石膏相比,高压硬石膏的拉曼光谱特征表现为SO_4对称伸缩振动(ν_1)从1 128.28 cm~(-1)突然下降至1 024.39 cm~(-1),同时对称弯曲振动(ν_2)分裂为441, 459和494 cm~(-1)三个峰,反对称伸缩振动(ν_3)分裂为1 136, 1 148, 1 158和1 173 cm~(-1)四个峰,反对称弯曲振动(ν_4)也分裂为598, 616, 646和671 cm~(-1)四个峰,可以作为判定硬石膏进入高压相态的有效标志。与硬石膏相比,高压硬石膏SO_4振动产生的拉曼峰数量更多、强度更低,表明影响SO_4振动的原子更多、分布更加复杂,这与高压硬石膏晶体结构(独居石结构,单斜晶系)的对称性比硬石膏(斜方晶系)更低相吻合。在硬石膏结构稳定的压力范围内(常压至2.3 GPa),硬石膏SO_4拉曼振动中除了ν_(2, 416)的振动频率变化不显著以外,其余振动均随着压力的升高以稳定的速率向高波数方向移动,同时谱峰的强度、形态和半高宽没有明显改变,从而保证了不同压力下硬石膏的拉曼峰具有一致的拟合误差和压力标定精度。同时,还通过方解石ν_(1, 1 085)拉曼峰随压力的变化速率、方解石向CaCO_3-Ⅱ以及CaCO_3-Ⅱ向CaCO_3-Ⅲ的相变压力对硬石膏压力标定结果进行检验,确定了硬石膏压标的可靠性。
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 ν_1 mode from 1 128.28 to 1 024.39 cm~(-1), and by splitting of the ν_2 mode into 441, 459 and 494 cm~(-1), ν_3 into 1 136, 1 148, 1 158 and 1 173 cm~(-1), and ν_4 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 ν_2～ν_4 vibrations into more bands indicated that the SO_4 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 SO_4 vibrations, except for the ν_(2, 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 ν_(1, 1 085) Raman peak position of calcite with pressure, and the phase transition pressures from calcite to CaCO_3-Ⅱ and from CaCO_3-Ⅱ to CaCO_3-Ⅲ.
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 ν_1 mode from 1 128.28 to 1 024.39 cm~(-1), and by splitting of the ν_2 mode into 441, 459 and 494 cm~(-1), ν_3 into 1 136, 1 148, 1 158 and 1 173 cm~(-1), and ν_4 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 ν_2～ν_4 vibrations into more bands indicated that the SO_4 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 SO_4 vibrations, except for the ν_(2, 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 ν_(1, 1 085) Raman peak position of calcite with pressure, and the phase transition pressures from calcite to CaCO_3-Ⅱ and from CaCO_3-Ⅱ to CaCO_3-Ⅲ.
引文
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[9] FU Pei-ge, ZHENG Hai-fei(付培歌, 郑海飞). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2013, 33(6): 1557.
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[11] Yuan X Y, Mayanovic R A. Applied Spectroscopy, 2017, 71(10): 2325 .
[12] Buzgar N, Buzatu A, Sanislav I V. Analele ?tiintifice ale Universit?ii “Al. I. Cuza” din Ia?i, 2009, 55: 5.
[13] YANG Yu-ping, ZHENG Hai-fei(杨玉萍, 郑海飞). Acta Mineralogica Sinica(矿物学报), 2005, 25(3): 299.
[14] Tolédano P, Dmitriev V. Ferroelectric, 1997, 191: 293.
[15] Liu L G, Mernagh T P. American Mineralogist, 1990, 75(7-8): 801.
[16] Bagdassarov N, Slutskii A B. Phase Transitions, 2003, 76(12): 1015 .
[2] Stephens D. Journal of Geophysical Research, 1964, 69: 2967.
[3] Borg I Y, Smith D K. Contribution to Mineralogy and Petrology, 1975, 50: 127.
[4] Ma Y M, Zhou Q, He Z, et al. Journal of Physics: Condensed Matter, 2007, 19: 425221.
[5] Bradbury S E, Williams Q. Journal of Physics and Chemistry of Solids, 2009, 70: 134.
[6] Fujii T, Ohfuji H, Inoue T. Physics and Chemistry of Minerals, 2016, 43: 353.
[7] Crichton W, Parise J, Antao S, et al. American Mineralogist, 2005, 90: 22.
[8] Bassett W, Shen A, Bucknum M, et al. Review of Scientific Instruments, 1993, 64: 2340.
[9] FU Pei-ge, ZHENG Hai-fei(付培歌, 郑海飞). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2013, 33(6): 1557.
[10] Pippinger T, Miletich R, Merlini M, et al. Physics and Chemistry of Minerals, 2015, 42: 29.
[11] Yuan X Y, Mayanovic R A. Applied Spectroscopy, 2017, 71(10): 2325 .
[12] Buzgar N, Buzatu A, Sanislav I V. Analele ?tiintifice ale Universit?ii “Al. I. Cuza” din Ia?i, 2009, 55: 5.
[13] YANG Yu-ping, ZHENG Hai-fei(杨玉萍, 郑海飞). Acta Mineralogica Sinica(矿物学报), 2005, 25(3): 299.
[14] Tolédano P, Dmitriev V. Ferroelectric, 1997, 191: 293.
[15] Liu L G, Mernagh T P. American Mineralogist, 1990, 75(7-8): 801.
[16] Bagdassarov N, Slutskii A B. Phase Transitions, 2003, 76(12): 1015 .