2002 年 12 巻 1 号 p. 28-33
Recent high-pressure studies using diamond anvil cell of methane hydrate are reviewed. Three high-pressure phases of methane hydrate were observed by x-ray diffraction and Raman spectroscopy up to 8 GPa in the present authors' study. The well-known cubic phase I decomposed into a hexagonal phase A and fluid at 0.8 GPa. The phase A transformed into an orthorhombic phase B at 1.6 GPa, and the phase B further transformed into another orthorhombic phase C at 2.1 GPa which survived above 7.8 GPa. The fluid solidified as ice VI at 1.4 GPa, and the ice VI transformed to ice VII at 2.1 GPa. The bulk moduli, K0, for the phase I, phase A, and phase C were calculated to be 7.4, 9.8, and 25.0 GPa, respectively. Comparison of the highpressure studies and the description of these high pressure structures were described in detail.