Raman scattering from the misfit-layer compounds SnNbS3 , PbNbS3 , and PbTiS3

Raman-scattering experiments have been carried out on misfit-layer compounds MT${\mathrm{S}}_{3}$ (M=Sn, Pb; T=Nb, Ti), in which two types of building layers, MS and T ${\mathrm{S}}_{2}$, are stacked alternately. The spectra obtained from these compounds are regarded as the superposition of the intralayer vibrations of individual layers, which indicates a weak interlayer interaction. The observed Raman shift of the intralayer modes of ${\mathrm{NbS}}_{2}$ relative to those of 2H-${\mathrm{NbS}}_{2}$ is interpreted in terms of a charge transfer from the MS layer to the ${\mathrm{NbS}}_{2}$ layer.