Raman study of phase transitions in compressed methane using moissanite anvil cells

Thorough investigations using Raman spectra of solid methane (CH(4)) were conducted using moissanite anvil cells in the range of 1-43 GPa at room temperature to identify high-pressure phases. Two interesting phases were uncovered, one with a narrow pressure range of 1 GPa centered at around 12.5 GPa and another with a range of 3 GPa centered at around 40.5 GPa. Our results do not support the existence of a phase transformation around 25 GPa. The high-quality Raman spectra, obtained by using single-crystal samples, narrow the boundaries of seven methane phases at pressures up to 43.2 GPa.