High-pressure experiments were performed to understand the structural evolution of methane hydrate (MH) up to 134 GPa using x-ray powder diffraction (XRD) and Raman spectroscopy with diamond anvil cells. XRD revealed the distinct changes in the diffraction lines of MH owing to phase transition from a guest-ordered state phase [MH-III(GOS)] to a new high-pressure phase (MH-IV) at 33.8–57.7 GPa. MH-IV was found to be stable up to at least 134 GPa without decomposition into solid methane and high-pressure ices. Raman spectroscopy showed the splits in the C–H vibration modes ν3 and ν1 of guest methane molecules in filled-ice Ih (MH-III) at 12.7 GPa and 28.6 GPa, respectively. These splits are caused by orientational ordering of guest methane molecules contained in the hydrate structure, as observed in a previous study. These results suggest that the structural evolution of the filled-ice structure of MH is caused by successive orientational ordering of guest methane molecules, thereby inducing changes in the host framework formed by water molecules.
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21 May 2020
Research Article|
May 21 2020
Structural evolution of methane hydrate under pressures up to 134 GPa
Hirokazu Kadobayashi
;
Hirokazu Kadobayashi
a)
1
National Institute for Materials Science (NIMS)
, Tsukuba, Ibaraki 305-0044, Japan
a)Present address: Hirokazu Kadobayashi National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan. Author to whom correspondence should be addressed: KADOBAYASHI.Hirokazu@nims.go.jp
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Hisako Hirai;
Hisako Hirai
2
Department of Environment Systems, Faculty of Geo-environmental Science, Rissho University
, Kumagaya, Saitama 360-0194, Japan
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Hiroaki Ohfuji;
Hiroaki Ohfuji
3
Geodynamics Research Center, Ehime University
, Matsuyama, Ehime 790-8577, Japan
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Michika Ohtake;
Michika Ohtake
4
National Institute of Advanced Industrial Science and Technology (AIST)
, Tsukuba, Ibaraki 305-8569, Japan
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Michihiro Muraoka;
Michihiro Muraoka
4
National Institute of Advanced Industrial Science and Technology (AIST)
, Tsukuba, Ibaraki 305-8569, Japan
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Suguru Yoshida;
Suguru Yoshida
4
National Institute of Advanced Industrial Science and Technology (AIST)
, Tsukuba, Ibaraki 305-8569, Japan
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Yoshitaka Yamamoto
Yoshitaka Yamamoto
4
National Institute of Advanced Industrial Science and Technology (AIST)
, Tsukuba, Ibaraki 305-8569, Japan
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a)Present address: Hirokazu Kadobayashi National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan. Author to whom correspondence should be addressed: KADOBAYASHI.Hirokazu@nims.go.jp
J. Chem. Phys. 152, 194308 (2020)
Article history
Received:
March 13 2020
Accepted:
May 03 2020
Citation
Hirokazu Kadobayashi, Hisako Hirai, Hiroaki Ohfuji, Michika Ohtake, Michihiro Muraoka, Suguru Yoshida, Yoshitaka Yamamoto; Structural evolution of methane hydrate under pressures up to 134 GPa. J. Chem. Phys. 21 May 2020; 152 (19): 194308. https://doi.org/10.1063/5.0007511
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