K. Kisoda et al., RAMAN-SCATTERING FROM MISFIT LAYER COMPOUNDS (RS),XTAS2(R-EQUIVALENT-TO-LA, CE, SM OR GD, S-EQUIVALENT-TO-SULFUR, X-SIMILAR-OR-EQUAL-TO-1.2), Journal of physics. Condensed matter, 7(27), 1995, pp. 5383-5393
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 mot
ion. 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 belo
w about 200 cm(-1) are ascribed to the intralayer modes of the RS laye
r and the main peaks higher than 200 cm(-1) are ascribed to the intral
ayer modes of the TaS2 layer. The E mode relevant to the TaS2 layer sh
ifts 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 mo
des of each layer, extra modes which show an anisotropy in the basal p
lane are observed at 360-370 cm(-1). These observations indicate that
the restoring forces for intralayer and interlayer interactions streng
then 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.