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.