High-pressure phases of SF6 up to 32Â GPa from X-ray diffraction and Raman spectroscopy

X-ray diffraction and Raman spectroscopy were employed to study the phase diagram of SF6 at pressures up to 32 GPa. The known phase transformation of SF6 phase I to phase II at around 2 GPa was confirmed. Discontinuities in the pressure dependence of the Raman frequencies and positions of X-ray reflections indicate further phase transitions at 10(1) and 19(1) GPa. The crystal structures of phases I and II were determined using single crystal X-ray diffraction. The structure of phase I corresponds to the “plastic” body-centred cubic low-temperature structure and the structure of phase II to the ordered monoclinic low-temperature structure. The bulk moduli of phase I and II were determined to be B0,I=6.3(2)GPa with BI′=4 (fixed) and B0,II=8.5(8)GPa with BII′=7.4(9), respectively. The linear compressibilities of phase II showed a slight anisotropy, which can be rationalised by consideration of the packing of the SF6 molecules.