Local electronic structure of Tl–Sn–Te compounds

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We show that the combined application of Mössbauer spectroscopy and X-ray photoelectron spectroscopy (XPS) provides a consistent picture of the local electronic structure in Tl 5Te 3, TlTe, Tl 2Te 3, Tl 4SnTe 3 and Tl 2SnTe 5. The results are discussed from a tight-binding calculation of the electronic populations. We show that values of the Tl 4f 7/2 core-level binding energy do not vary noticeably for the different compounds in agreement with the close values of the calculated Tl average charges. The results obtained by both the XPS and 125Te Mössbauer spectroscopy are consistent with the existence of two types of Te atoms with very different atomic charges due to the differences in the number of Te 5p electrons. The variations of the Te charge are explained from changes in the nature of the Te nearest neighbors: Tl, Sn and Te as a function of the stoichiometry. Finally, we show that values of the 119Sn Mössbauer isomer shift and the Sn 4d 5/2 core-level binding energy both increase from Tl 2SnTe 5 to Tl 4SnTe 3 in agreement with the increase of the calculated number of Sn 5s electrons and the decrease of the calculated number of Sn 5p electrons, respectively. These changes are related to the differences between the Sn local environments of the two ternary compounds.