Local electronic structure of Tl-Sn-Te compounds

We show that the combined application of Mossbauer spectroscopy and X-ray p hotoelectron spectroscopy (XPS) provides a consistent picture of the local electronic structure in Tl5Te3, TlTe, Tl2Te3, Tl4SnTe3 and Tl2SnTe5. The re sults are discussed from a tight-binding calculation of the electronic popu lations. 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 clos e values of the calculated Tl average charges. The results obtained by both the XPS and Te-125 Mossbauer spectroscopy are consistent with the existenc e of two types of Te atoms with very different atomic charges due to the di fferences 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 Sn-119 Mossbauer isomer shift and the Sn 4d(5/2) core-level binding energy both increase from Tl2SnTe5 to Tl4SnTe3 in agreement with the increa se of the calculated number of Sn 5s electrons and the decrease of the calc ulated number of Sn 5p electrons, respectively. These changes are related t o the differences between the Sn local environments of the two ternary comp ounds. (C) 1999 Elsevier Science Ltd. All rights reserved.