Stage dependence of phonons in misfit layer compounds (MS)(NbS2)(n) (M=Sn,Pb; n=1,2)

Misfit layer compounds (MS)(NbS2)(n) (M = Sn,Pb; n = 1, 2) are composed of two types of layers MS and NbS2. Raman spectra of these compounds have been measured for stage-1 (n = 1) and stage-2 (n = 2) compounds and compared with those of pristine NbS2 and other misfit layer compounds. The intralayer E modes of the NbS2 layer for (MS)(NbS2)(n) shifts upwards relative to 2H- and 3R-NbS2 and the amount of the shift is larger for the stage-1 compounds than the stage-2 compounds. This result is interpreted in terms of the charge transfer (CT) from the MS layer to the NbS, layer. The extra phonon modes observed for (RS)(NbS)(2) (R = La,Ce) which become Raman active by the breakdown of the mirror symmetry of the NbS2 layer are not observed for (PbS)(NbS2)(2) because the amount of CT is considerably smaller for the Pb compounds than the La and Ce compounds.