Lattice dynamics of BaClF and SrClF

The lattice dynamics of tetragonal BaClF and SrClF have been worked out in detail on the basis of a shell model. The shell model parameters obtained from the transfer of corresponding parameters from the respective fluorides gives rise to long wavelength optic phonons in good agreement with the experimental results. Calculations have been made of the phonon dispersion relations, elastic constants, phonon density of states, temperature variation of specific heats and the lattice phonon moments.The mean square displacements of the various ions in these systems have also been computed over a wide range of temperature. Comparison with the available X-ray experimental data on thermal vibration parameters shows the agreement to be satisfactory.