Investigating the Shock Induced Phase Transition in Single Crystal Barium Flouride.

Barium fluoride (BaF₂) is a model ionic solid that crystallizes in the cubic fluorite structure (Fm3̄m) with eightfold cation coordination. Under static compression, BaF₂ undergoes well-characterized transitions to a cotunnite-type phase (Pnam) near 3 GPa and a Ni₂In-type phase (P6₃/mmc) near 13 GPa, involving volume collapses of 8–9% and eventual metallization near 33 GPa. To explore the response of BaF₂ under rapid compression, we conducted plate-impact shock experiments on single crystals across a wide range of stresses. Laser interferometry was used to record particle velocity histories and determine stress–density states under dynamic loading. The measured wave profiles reveal multiple-wave structures consistent with the elastic precursor and subsequent transformation waves associated with the fluorite-to-cotunnite and higher-pressure transitions. These results provide direct evidence of pressure-induced polymorphism under shock loading and new constraints on the kinetics and stability limits of high-density BaF₂ phases under extreme dynamic conditions.