Structural changes of filled ice Ic structure for hydrogen hydrate under high pressure
Structural changes of filled ice Ic structure for hydrogen hydrate under high pressure
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DOI：
10.1063/1.3013440
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发表时间：
2008-12-14
影响因子：
4.4
通讯作者：
Yagi, Takehiko
中科院分区：
文献类型：
--
作者：
Machida, Shin-ichi;Hirai, Hisako;Yagi, Takehiko
采用金刚石砧池，在0.1 ~ 80.3 GPa的室温压力范围内，对填充冰Ic结构的水合氢进行了高压实验。原位x射线衍射（XRD）分析表明，在35 ~ 40和55 ~ 60 GPa的温度下，水合物的结构发生了变化，高压相在至少80.3 GPa的温度下仍然存在。拉曼光谱分析表明，在40和60 GPa左右，氢水合物中氢分子的振动模式发生了变化，这与XRD的结果一致。在40 GPa左右，构成骨架的宿主水分子分子间距离达到了水分子氢键对称的临界距离，表明在40 GPa左右发生了氢键对称。对称化可能会引起填充冰结构的一些结构变化。此外，55 ~ 60 GPa以上高压相的存在表明，水合物中可能存在比填充冰Ic更致密的结构。
High-pressure experiments of hydrogen hydrate, filled ice Ic structure, were performed using a diamond-anvil cell in the pressure range of 0.1-80.3 GPa at room temperature. In situ x-ray diffractometry (XRD) revealed that structural changes took place at approximately 35-40 and 55-60 GPa, and that the high-pressure phase of hydrogen hydrate survived up to at least 80.3 GPa. Raman spectroscopy showed that the changes in vibrational mode for the hydrogen molecules in hydrogen hydrate occurred at around 40 and 60 GPa, and these results were consistent with those of the XRD. At about 40 GPa, the intermolecular distance of host water molecules consisting the framework attained the critical distance of symmetrization of the hydrogen bond for water molecules, which suggested that symmetrization of the hydrogen bond occurred at around 40 GPa. The symmetrization might introduce some structural change in the filled ice Ic structure. In addition, the existence of the high-pressure phase above 55-60 GPa implies that a denser structure than that of filled ice Ic may exist in hydrogen hydrate.