TY - JOUR
T1 - Structural evolution of methane hydrate under pressures up to 134 GPa
AU - Kadobayashi, Hirokazu
AU - Hirai, Hisako
AU - Ohfuji, Hiroaki
AU - Ohtake, Michika
AU - Muraoka, Michihiro
AU - Yoshida, Suguru
AU - Yamamoto, Yoshitaka
N1 - Funding Information:
The authors are thankful to Dr. K. Komatsu for fruitful discussion. This research was partly supported by a Grant-in-Aid for JSPS Fellows (Grant No. 19J01467) and Early-Career Scientists (Grant No. 19K14815) from the Japan Society for the Promotion of Science. This research was also supported by the Joint Usage/Research Center PRIUS, Ehime University, Japan.
Publisher Copyright:
© 2020 Author(s).
PY - 2020
Y1 - 2020
N2 - 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 v3 and v1 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.
AB - 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 v3 and v1 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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U2 - 10.1063/5.0007511
DO - 10.1063/5.0007511
M3 - Article
C2 - 33687263
AN - SCOPUS:85093365323
SN - 0021-9606
VL - 152
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 19
M1 - 194308
ER -