A RAMAN-STUDY OF THE MISFIT LAYER COMPOUNDS, (SNS)1.17NBS2 AND (PBS)1.18TIS2

The Raman and resonance Raman spectra (850-20 cm-1) of powdered samples of the misfit layer compounds (SnS)1.17NbS2 and (PbS)1.18TiS2 at 300 K have been investigated. In partial agreement with structural data, vibrational assignments are proposed for most of the internal modes of the 'MS' and 'TS2' sublattices and the band wavenumbers are compared to those in the 2H-NbS2 and IT-TiS2 prototypes, in order to understand the inter-action in which 'MS' acts as the donor part of the structure. Owing to their incommensurate modulated structures along the {xi00} direction, characteristic Raman bands at 197 cm-1 ('SnNbS3') or 203 cm-1 ('PbTiS3'), assigned to mostly TA or LA type modes, become Raman active due to a zone folding mechanism. New information about the lattice dynamics in the 'TS2' sublayers is thus obtained.