HIGH-PRESSURE RAMAN-STUDY OF CARBON TETRAFLUORIDE UP TO 8 GPA

High-pressure Raman spectra of carbon tetrafluoride (CF4) have been measured up to 8 GPa at 300 K in a gasketed diamond anvil cell. The pressure dependence of four intramolecular vibrations has been investigated. The liquid-solid I, solid I-II and solid II-III phase transitions at respective pressures 1.86 GPa, 2.84 GPa and 3.5 GPa are presented by the splitting of vibrational modes and the drastic change in Raman band widths. The observed solid I and II phases correspond to plastic (non-cubic) and monoclinic phases, respectively, that also appear at low temperatures and atmospheric pressure. The solid III phase above 3.5 GPa is a new phase. These transition pressures are supported by the good agreement with those obtained by extrapolation (to 300 K) of phase boundaries previously determined at low temperatures.