Phonons in layered compounds

Layer compounds exhibit highly anisotropic structural and elastic propertie s. They are characterized by rather rigid layers, loosely stacked together perpendicular to each other. Accordingly, the phonon dispersion of layered compounds are characterized by low lying inter-layer modes and high-frequen cy intra-layer modes. Intercalation compounds composed of a regular sequenc e of host and guest layers provide a playground for the investigation of th e layer lattice dynamics by systematically changing the guest species and t he number of guest layers per unit cell. In this contribution a brief overv iew of some characteristic features of the lattice dynamics of layered comp ounds is provided.