Raman scattering from the misfit-layer compounds ${\mathrm{SnNbS}}_3$, ${\mathrm{PbNbS}}_3$, and ${\mathrm{PbTiS}}_3$

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.