ON THE RAMAN SHIFT IN MISFIT LAYER COMPOUNDS OF METAL-DICHALCOGENIDES(MX)(TX2) - AN EFFECT OF THE CHARGE-TRANSFER ON THE INTRALAYER NONCENTRAL FORCES

In the misfit layer compounds of metal-dichalcogenides (MX)(TX2), ther e are two intense Raman bands, which have been ascribed as their origi ns to the in-plane and the out-of-plane vibrations in the host layer c ompounds. It is commonly observed that the frequency of the in-plane m ode is appreciably increased, while that of the out-of-plane mode is a lmost unchanged, in the misfit layer compounds. The mechanism is inves tigated by means of the classical lattice dynamics. It is found that c ompetition between increasing central forces and decreasing noncentral forces in the host layer is the cause of this change. In the misfit l ayer compounds, electrons are donated to the host layer, further filli ng the conduction band. Filling that band makes the distribution of th e valence electrons more spherical, which eliminates the angle depende nce on the adiabatic potential. (C) 1997 Elsevier Science Ltd.