The electronic structure of five antimony chalcogenides, Sb${\mathrm{I}}_3$, ${\mathrm{Sb}}_2$${\mathrm{Te}}_3$, SbTeI, TlSb${\mathrm{S}}_2$, and ${\mathrm{Tl}}_3$Sb${\mathrm{S}}_3$, is investigated. Information from x-ray diffraction, Mössbauer spectroscopy, electrical measurements, and photoemission spectroscopy is combined with band-structure calculations to get a coherent picture of these materials. The chemical notion of the asymmetry and delocalization of the $5s^2$ antimony lone pair is given a quantitative interpretation both from the full band-structure calculation and from a simple molecular description.

• Received 3 August 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.2471