TRANSPORT AND OPTICAL-PROPERTIES OF PBTE1-XSX (X=0.02 AND X=0.05) MIXED-CRYSTALS

Far-infrared and Raman scattering spectra as well as galvanomagnetic m easurements of PbTe1-xSx (x = 0.02 and 0.05) mixed crystals in the tem perature range from IO to 300 K are presented. The far-infrand reflect ivity spectra an analysed using a fitting procedure based on the plasm on-phonon interaction model. Galvanomagnetic and far-infrared measurem ents indicate the existence of a phase transition at about T-c = 60 K for x = 0.05, whereas for samples with x = 0.02 the phase transition i s not observed. Also, it is found that the long-wavelength optical pho non modes of these mixed crystals show a ''two-mode'' behaviour.