A Raman study of the misfit layer compounds, (SnS)_1.17NbS₂ and (PbS)_1.18 TiS₂

Abstract

Abstract The Raman and resonance Raman spectra (850–20 cm −1 ) of powdered samples of the misfit layer compounds (SnS) 1.17 NbS 2 and (PbS) 1.18 TiS 2 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 ‘TS 2 ’ sublattices and the band wavenumbers are compared to those in the 2H‐NbS 2 and IT‐TiS 2 prototypes, in order to understand the interaction in which ‘MS’ acts as the donor part of the structure. Owing to their incommensurate modulated structures along the {ξ00} direction, characteristic Raman bands at 197 cm −1 (‘SnNbS 3 ’) or 203 cm −1 (‘PbTiS 3 ’), 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 ‘TS 2 ’ sublayers is thus obtained.