Pressure‐induced phase transitions and anharmonicity study of alkaline‐earth fluorides

Room temperature measurements of Raman scattering under hydrostatic pressure in a diamondanvil cell have shown that the cubic‐to‐orthorhombic (β → α) phase transition in CaF 2 and BaF 2 occurs at (8.5 ± 0.2) and (2.3 ± 0.2) GPa, respectively. The pressure dependence of the observed phonons in the α‐phase as well as their symmetry assignment based on a comparison to other fluorite‐structure crystals is presented. Anharmonic processes are shown to be small but not negligible and of the same nature in all alkaline‐earth fluorides. It is established that the β → α and α → β transition pressures show a linear dependence on the inverse volume of the unit cell for the alkaline‐earth fluorides CaF 2 , SrF 2 , and BaF 2 .