Lattice Dynamics of Transition-Metal Trichlorides

Abstract

The phonon dispersion curves of layered compounds, ScCl₃ and CrCl₃, are calculated using the simple shell model. The parameters are determined so as to reproduce the nine phonon frequencies observed by infrared and Raman spectroscopy. The calculated phonon dispersion curves reveal features characteristic of layered compounds, namely the dispersion along the c-axis is very small compared with the dispersion in the c-plane. The characters of the phonon modes at the center of the Brillouin zone are studied in detail and the results are discussed in connection with the structural phase transition of TiCl₃.