Electronic properties of the crystalline phases of theSb2S3−Tl2Ssystem

The electronic properties of the crystalline phases of the ${\mathrm{Sb}}_2{\mathrm{S}}_3{-\mathrm{T}\mathrm{l}}_2\mathrm{S}$ system are investigated both experimentally and theoretically. Experimental data obtained by x-ray photoelectron spectroscopy and ${}^{121}\mathrm{Sb}$ Mössbauer spectroscopy are reported and analyzed from tight-binding calculations, which are used here because of the complexity of the materials. The main features of the x-ray photoelectron valence bands and S $K\beta$ emission spectra are identified. The binding energy of the S ${2p}_{3/2}$ core level is found to decrease from ${\mathrm{Sb}}_2{\mathrm{S}}_3$ to ${\mathrm{Tl}}_2\mathrm{S}$ in agreement with the variations of the calculated S charges. We show that the ${}^{121}\mathrm{Sb}$ Mössbauer isomer shift and the surface of the prepeak observed in x-ray-absorption spectra at the Sb $L_{\mathrm{III}}$ edge can be linearly correlated because they are both strongly dependent on the Sb $5s$ electron population. Finally, analytical expressions of the numbers of Sb and S valence electrons are derived from simple molecular calculations. These expressions provide rather simple explanations for the observed main trends in the variations of the experimental results in terms of local structural changes.