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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，具有金红石型或改性金红石型晶体结构以及它们之间固溶体的矿物端元相（δ-AlOOH相、H相和stishovite）可以储存大量水，并在与地球下地幔相关的高压和高温下保持稳定。已经提出了Al-H电荷耦合取代（Si4+->Al3++H+）来解释其中一些相的存储容量。然而，如果这种替代占主导地位，在最近的一些例子中发现的H+量与预期值不匹配，并且很难单独用这种机制解释辉锑铅矿中更大的储水量。提出了一种八面体形式的类水石榴石取代（Si4+->4H（+））来解释无铝富水辉石中的质子掺入。然而，在这一阶段，OH的高压结构行为尚未被测量。在这项研究中，我们报告了在3.2+/-0.5 wt%水（高达55 GPa）的情况下，对无铝含水锑铅矿进行的高压拉曼光谱测量。在环境压力下，我们发现该相中的OH拉伸模式的频率介于低水铝锑铅矿和δAlOH中的频率之间，表明这两种情况之间的氢键中间强度。减压至1bar后，我们观察到类似于无水和含水锑铅矿的红外激活模式，表明晶体结构中存在的硅缺陷可以激活非激活模式。对于晶格和OH拉伸模式，我们的数据显示，在24到28 GPa的压力下发生了一系列变化，表明存在相变（可能是CaCl2型）。当我们的晶格从正态到正态的移动显示出不同的行为。我们所有的光谱

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