Pressure-Induced Phase Transitions in Solids: BaF2

Similarities between the pressure dependences of the elastic constants of Ba${\mathrm{F}}_2$ and RbI suggested that a pressure-induced phase transition should obtain in Ba${\mathrm{F}}_2$. This transition has been observed. With increasing pressure at 295 °K the transition occurs at 26.8 kbar. The transition pressure decreases with increasing temperature, and at sufficiently high pressure the transition can be induced by raising the temperature. The possible lattice dynamical nature of the transitions in RbI and Ba${\mathrm{F}}_2$ is discussed.