RAMAN SCATTERING FROM MISFIT LAYER COMPOUNDS (RS),XTAS2(R-EQUIVALENT-TO-LA, CE, SM OR GD S-EQUIVALENT-TO-SULPHUR X-SIMILAR-OR-EQUAL-TO-1.2)

摘要

Polarized Raman scattering experiments on misfit layer compounds (RS)(x)TaS2 (R = La, Ce, Sm or Gd; S = sulphur; x similar or equal to 1.2) have been carried out in order to investigate the effect of the charge transfer (CT) from an RS layer to a TaS2 layer on the vibrational motion. The mode assignment is made by comparing the spectra of(RS)xTaS(2) with those of 2H-TaS2 and (RS)(x)NbS2. The modes at frequencies below about 200 cm(-1) are ascribed to the intralayer modes of the RS layer and the main peaks higher than 200 cm(-1) are ascribed to the intralayer modes of the TaS2 layer. The E mode relevant to the TaS2 layer shifts upwards by about 40 cm-1 relative to the corresponding mode in 2H-TaS2 while the A mode hardly shifts. In addition to the intralayer modes of each layer, extra modes which show an anisotropy in the basal plane are observed at 360-370 cm(-1). These observations indicate that the restoring forces for intralayer and interlayer interactions strengthen owing to the CT. The two-phonon Raman band is observed at higher frequencies than that of 2H-TaS2. The comparison with the spectra of (RS)(x)NbS2 shows that the amount of the CT in (RS)(x)TaS2 is less than that in (RS)(x)NbS2. [References: 18]