STAGING AND INTERLAYER INTERACTION IN THE MISFIT-LAYER COMPOUNDS (RS)(N)NBS2 (R=LA,CE, N=0.6, 1.2) STUDIED BY RAMAN AND INFRARED SPECTROSCOPIES

Raman-scattering and infrared reflection measurements on misfit-layer compounds (RS)(n)NbS2 (n=0.6,1.2; R=La,Ce) have been carried out in or der to investigate the interlayer interaction and its relation to the charge transfer from the RS layer to the NbS2 layer. It is found that the intralayer modes of the NbS2 layer in (RS)(n)NbS2 are considerably upshifted from those of a pristine NbS2 crystal. Further, some extra modes are observed. These facts indicate a strong interlayer interacti on in these compounds. The modes corresponding to the intralayer vibra tions of the NbS2 layer are less perturbed for the stage-2 (n=0.6) com pounds than for the stage-1 (n=1.2) compounds owing to the difference of the amount of the charge transfer. However, the A'(2) (421 cm(-1)) mode, which is Raman inactive in an isolated NbS2 layer, appears stron gly for the stage-2 compounds. This result is interpreted in terms of the breakdown of the mirror symmetry of the NbS2 layer in the stage-2 compounds caused by the intercalation of the RS layer.