Lattice Dynamics of Potassium Halides (KCl, KBr and KI)

Abstract

To investigate the lattice dynamics of potassium halides a newly proposed 7-parameter bond-bending force model (BBFM) is used. The total potential energy of the system incorporates the short-range forces (radial+bond-bending) as well as the long range Coulombic interactions. The 7 parameters employed in the present treatment are determined by making use of the experimental values of three elastic constants, four critical point phonon frequencies and the lattice equilibrium condition. The model has been applied to calculate the phonon dispersion relations, phonon density of states and the Debye-characteristic temperatures (θ_D) of KCl, KBr, and KI. Theoretical results have been compared with the available experimental data. It is observed that the agreement between theory and experiment is very good and thus gives a confidence in this approach. The remarkable features pertaining to the physical significance of the model have been discussed.