X-ray absorption fine structure studies of the local structure of large Pb and Sn substitutional impurities in GeTe were carried out. The local environment of these atoms in Ge0.9Pb0.1Te and Ge0.85Sn0.15Te solid solutions was shown to be strongly distorted in comparison with that in binary PbTe and SnTe compounds. The neighboring Te atoms were found at two distances, 3.06 and 3.27 A (for Pb), and 2.97 and 3.18 A (for Sn atoms). For both impurities the shortest distance appeared to be substantially shorter than that in corresponding binary compounds with the same overall coordination. The off-centering of Pb and Sn impurities is explained by participation of their deeply lying 6s2 and 5s2 lone electron pairs in chemical bonding in the condition of strong local stress created by these impurities in the lattice.
Keywords: X-ray absorption spectroscopy, EXAFS, ferroelectric phase transitions, doping, local environment, germanium telluride, lead, tin, chemical bonding