Lattice dynamics of fluoride scheelites: II. Inelastic neutron scattering in and modelization

A general view of the fluoride scheelite lattice dynamical properties is proposed. The symmetry properties of the vibrations and the symmetry-adapted eigenvectors of the scheelite structure have been determined for the most important directions of the Brillouin zone, namely , and . The low-frequency phonon spectrum along these three directions has been measured by inelastic neutron scattering. The corresponding data, together with the measured sound velocities and the Raman- and infrared-active phonon frequencies, are described in the framework of a rigid ion model. The average error between experimental results and calculated frequencies is less than 5%. The most important normal modes of vibration and the one-phonon density of states are deduced.