High-pressure phase transition of magnesium fluoride under shock compression

Shock compression was applied to single-crystal magnesium fluoride (MgF₂) in the (100) and (111) directions by using guns, and the propagating shock wave profiles were measured. In the (100) compression, a kink originating from the phase transition was observed on the shock wave front. The shock compression state after the phase transition was in good agreement with the compression curve of the PdF₂ phase predicted from theoretical calculations. In the (111) compression, although the formation of a multi-wave structure associated with the phase transition was not observed on the shock wave front, the shock compression state asymptotically approaches the theoretical compression curve of the PdF₂ phase as the shock pressure increases. X-ray diffraction measurements of polycrystalline MgF₂ under shock compression confirmed the formation of the PdF₂ phase under shock compressed state. It was also confirmed that the phase transition to the α-PbO₂ structure was observed during the pressure release process, instead of back-transition to the initial rutile structure.