OPTICAL REFLECTIVITY AND TRANSMISSIVITY OF MISFIT LAYER COMPOUNDS (MS)(N)TS2(T=TA, NB, M=PB, SM, TB, 1.08-LESS-THAN-N-GREATER-THAN-1.23)

The room temperature transmission and reflection behaviour of misfit l ayer compounds (MLCs) (MS)(n)TS2 (T=Nb, Ta; M=Pb, Sm, Tb) were investi gated in the spectral range between 1000 and 20000 cm(-1) for incident light normal to the layered structure (k perpendicular to(001)). A ch aracteristic near infrared transmission window (TW) is observed betwee n the Drude free carrier threshold (4000 cm(-1) <w(0)<6000 cm(-1)) and the onset of stronger interband transitions (above 13000 cm(-1)). Eva luations of the absorption profiles show an interband absorption super imposed on the free carrier absorption in the TW which are related to transitions involving states in the conduction band (or conduction ban ds). Values of w(0) are found to be slightly smaller for E parallel to b compared to E parallel to a (parallel to the incommensurate directi on) polarized spectra for all compounds under study. This effect is in terpreted in terms of slightly smaller effective masses for the optica l conductivity for the E parallel to a components. The temperature dep endence (213 to 423 K) of the free carrier reflectivity for (PbS)(1.13 )TaS2 shows a linear increase of the damping parameter with temperatur e both for E parallel to a and E parallel to b. This is suggested to b e due to ordinary electron-phonon scattering of the free carriers. Ref lection spectra for E parallel to c indicate wo values of about 1500 c m(-1) for (SmS)(1.19)TaS2 ((TbS)(1.21)NbS2) and below 1300 cm(-1) for (PbS)(1.13)TaS2((PbS)(1.21)NbS2).