Lattice dynamics and inelastic neutron scattering studies ofMFX(M=Ba,Sr, Pb;X=Cl,Br, I)

Abstract

We report lattice dynamical calculation of technologically important matlockite structured compounds $M\mathrm{F}X$ $[M(\mathrm{Ba},$ Sr, Pb); $X(\mathrm{Cl},$ Br, I)] using a transferable interatomic potential based on a shell model. Our model is validated by the inelastic neutron scattering measurement of the phonon density of states for BaFCl carried out using the triple axis spectrometer at Trombay. We have further exploited this model for the calculation of high-pressure and high-temperature thermodynamic properties of these compounds which are found to be in good agreement with various experimental data, as available in the literature. The calculations provide a theoretical understanding of the elastic constants, equation of state, phonon dispersion relations and density of states, thermal expansion, specific heat, Debye temperature, and anisotropic thermal parameters of these materials.