X-ray diffraction investigations of CaF₂ at high pressure

Synchrotron-radiation X-ray diffraction studies of CaF₂ at high pressures have been performed on a powder sample up to 45 GPa and on a single-crystal sample up to 9.4 GPa. The bulk modulus of the low-pressure phase was determined to be B₀ = 87 (5) GPa. A phase transition was observed at about 9.5 GPa. The transition is accompanied by a volume contraction of 11%. The high-pressure phase is orthorhombic PbCl₂ type (space group Pbnm). The sample only partially reverts to the low-pressure phase upon release of pressure.