Phase changes of solid methane under high pressure up to 86 GPa at room temperature

High pressure studies of solid methane were performed using diamond anvil cells in the pressure range of 0.5-86 GPa. X-ray diffractometry and Raman spectroscopy revealed two high pressure phases above 35 GPa. The results suggested that the observed high pressure phases have a fundamental structure similar to that of a reported high pressure phase, but they exhibit the orientational ordering of molecules in a different manner. An intermediate metastable phase was found between known phase A and phase B, which showed a structure close to that of phase B but showed rotation of molecules close to that of phase A. (c) 2008 Elsevier B. V. All rights reserved.