Abstract
High-pressure Raman and Brillouin measurements have been made for single crystalline methane-ethylene hydrate (MEH) at 293K. We have found that two pressure-induced phase transformations occur at 1.7GPa and 2.1GPa, and MEH decompose by associating with the formation of polyethylene above 3.3GPa. The initial cubic sI phase of MEH remains stable up to 1.7GPa, which is twice wide pressure range of the methane hydrate sI phase. In this sI phase of MEH, the cage occupancies by methane and ethylene molecules, structural stability, and elastic properties are investigated from the results of Raman and Brillouin measurements.
