RAMAN-STUDY AND LATTICE-DYNAMICS CALCULATIONS OF MISFIT LAYERED COMPOUNDS - (PBS)(1.18)TIS2 AND (PBS)(1.12)VS2

The UV-visible (340-800 nm), Raman and resonance Raman spectra (10-900 cm(-1)) of powered samples or the two title misfit compounds were inv estigated. In agreement with X-ray data, vibrational assignments are p roposed for the internal modes of the ''PbS'' and ''TS2'' sublattices (TiS2 or VS2) and the latter ones are compared to those in the 1T-TiS2 polytype in order to appreciate the interactions due to the ''PbS'' d onor part of the structures. Owing to their incommensurate structures, new resonance enhanced Raman signals are observed and explained by th e k = +/- q() selection rules (q(*) is the modulation vector); these observations are confirmed by VFF lattice calculations which reproduce the essential experimental data.