An EXAFS study of the local structure of the Pb_xSn_1-xS solid solution

A.I. Lebedev, I.A. Sluchinskaya, I.H. Munro

Moscow State University, Vorob'evy gory, Moscow, 119899 Russia
Daresbury Laboratory, Warrington, WA4 4AD UK

The local environment of Pb atoms in the Pb_xSn_1-xS solid solutions with cubic and orthorhombic structure was studied by EXAFS spectroscopy. The shortest Pb-S distance in samples with orthorhombic structure was found to be smaller by 0.2 A than that in cubic-lattice samples, which is a sign of stereochemical activity of the 6s² lone electron pair of a Pb atom. The metal atom arrangement reveals strong short-range order, which results in the formation of -Pb-Sn-Pb-Sn-... zigzag chains aligned with the c axis (in the Pbnm system) in orthorhombic samples. It was shown that the onset of such short-range order in Pb_0.5Sn_0.5S can initiate the formation of superstructures belonging to the C_2v⁷ or C_2v² space groups.

Keywords: x-ray absorption spectroscopy, lead tin sulfide sulphide, semiconductor solid solutions, synchrotron radiation

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