ELECTRONIC-PROPERTIES OF THE CRYSTALLINE PHASES OF THE SB2S3-TL2S SYSTEM

The electronic properties of the crystalline phases of the Sb2S3-Tl2S system an investigated both experimentally and theoretically. Experime ntal data obtained by x-ray photoelectron spectroscopy and Sb-121 Moss bauer spectroscopy are reported and analyzed from tight-binding calcul ations, which are used here because of the complexity of the materials . The main features of the x-ray photoelectron valence bands and S K b eta emission spectra are identified. The binding energy of the S 2p(3/ 2) core level is found to decrease from Sb2S3 to Tl2S in agreement wit h the variations of the calculated S charges. We show that the Sb-121 Mossbauer isomer shift and the surface of the prepeak observed in x-ra y-absorption spectra at the Sb L-III edge can be linearly correlated b ecause they are both strongly dependent on the Sb 5s electron populati on. Finally, analytical expressions of the numbers of Sb and S valence electrons are derived from simple molecular calculations. These expre ssions provide rather simple explanations for the observed main trends in the variations of the experimental results in terms of local struc tural changes.