The temperature dependence of elastic constants of some fluorite-structure crystals (namely ${\mathrm{BaF}}_2$, ${\mathrm{PbF}}_2$, and ${\mathrm{SrCl}}_2$) has been investigated by means of potential models that include the effects of three-body interactions (TBI) and lattice anharmonicity arising from thermal-phonon pressure. The agreement between the experimental and present theoretical model I (with TBI) is better than that obtained from model II (without TBI) and is comparable with those calculated from measured Brillouin-scattering frequencies [Catlow et al., J. Phys. C 11, 3179 (1978)]. It has been found that the lattice anharmonicity is responsible for an anomalous change in elastic constants with temperature for the fluorites.

• Received 23 January 1989

DOI:https://doi.org/10.1103/PhysRevB.39.13493