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首页> 外文期刊>The American mineralogist >Raman spectroscopy of water-rich stishovite and dense high-pressure silica up to 55 GPa
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Raman spectroscopy of water-rich stishovite and dense high-pressure silica up to 55 GPa

机译：富含水的脊柱管和致密的高压二氧化硅的拉曼光谱，高达55 GPA

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Recent studies have shown that mineral end-member phases (delta-AlOOH phase, phase H, and stishovite) with rutile-type or modified rutile-type crystal structures and solid solutions between them in the MgO-Al2O3-SiO2 system can store large amounts of water and can be stable at high pressures and high temperatures relevant to the Earth's lower mantle. The Al-H charge-coupled substitution (Si4+ -> Al3+ + H+) has been proposed to explain the storage capacity found in some of these phases. However, the amount of H+ found in some recent examples does not match the expected value if such substitution is dominant, and it is difficult to explain the larger water storage in stishovite with such a mechanism alone. An octahedral version of the hydrogarnet-like substitution (Si4+ -> 4H(+)) has been proposed to explain the incorporation of protons in Al-free, water-rich stishovite. Yet, the high-pressure structural behavior of OH in this phase has not yet been measured. In this study, we report high-pressure Raman spectroscopy measurements on Al-free hydrous stishovite with 3.2 +/- 0.5 wt% water up to 55 GPa. At ambient pressure, we find that the OH stretching modes in this phase have frequencies lying in between those in low-water aluminous stishovite and those in delta-AlOOH, suggesting a strength of the hydrogen bonding intermediate between these two cases. After decompression to 1 bar, we observe modes that are similar to the IR-active modes of anhydrous and hydrous stishovite, suggesting that the existence of Si defects in the crystal structure can activate the inactive modes. For both lattice and OH-stretching modes, our data show a series of changes at pressures between 24 and 28 GPa suggesting a phase transition (likely to CaCl2-type). While some of the lattice mode behaviors are similar to what was predicted for the AlOOH polymorphs, the OH mode of our hydrous stishovite shows a positive frequency shift with pressure, which is different from delta-AlOOH. All our spectra
机译：最近的研究表明，在MgO-Al2O3-SiO2系统中，矿物端构件（Delta-AlOOH相，H相，H和脊柱杆菌）具有金红石型或改性的金红石型晶体结构和它们之间的固溶溶液可以存储大量水可以稳定，高压和与地球下部地幔相关的高温。已经提出了Al-H充电耦合替代（Si4 + - > Al3 + H +）以解释其中一些阶段中的存储容量。然而，如果这种替代是显性的，则在一些最近的实施例中发现的H +的量与预期值不匹配，并且很难用这种机制解释脊柱岩中的较大储水。已经提出了八面体版的水慢性替代（Si4 + - > 4h（+）），以解释在无富含玻璃水中的质子的质子。然而，尚未测量该阶段的高压结构行为。在这项研究中，我们在无含水脊柱岩中报告高压拉曼光谱测量，3.2 +/- 0.5wt％水，高达55gPa。在环境压力下，我们发现该阶段的OH拉伸模式具有伴随在低水铝柱系之间的频率和Delta-Alooh的频率，这表明这两种情况之间的氢键中间体的强度。在减压到1巴后，我们观察类似于无水和含水脊柱管道的IR-活性模式的模式，表明晶体结构中的Si缺陷的存在可以激活非活动模式。对于晶格和OH拉伸模式，我们的数据显示了24至28个GPA的压力的一系列变化，表明相转变（可能对CaCl2型）。虽然一些晶格模式行为类似于预测的Alooh多晶型物的行为，但是我们垂湿的脊柱管道的OH模式显示了压力的正频率，这与Delta-Alooh不同。我们所有的光谱

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