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Real structure of Ge 4 Bi 2 Te 7 : refinement on diffuse scattering data with the 3D‐ΔPDF method
Author(s) -
Urban Philipp,
Simonov Arkadiy,
Weber Thomas,
Oeckler Oliver
Publication year - 2015
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576714027824
Subject(s) - vacancy defect , atom (system on chip) , metastability , scattering , diffraction , maxima , bragg's law , molecular physics , materials science , crystallography , condensed matter physics , chemistry , optics , physics , art , organic chemistry , performance art , computer science , art history , embedded system
Metastable Ge 4 Bi 2 Te 7 is highly disordered; the average structure corresponds to the rocksalt type. The diffraction pattern shows diffuse streaks interconnecting Bragg reflections along all cubic 〈111〉 directions. These streaks exhibit satellite‐like maxima and arise from vacancy ordering in non‐periodically spaced defect layers. The atom layers near these vacancy layers are displaced with respect to the average structure: they tend to form α‐GeTe‐type double layers. The three‐dimensional difference pair distribution function (3D‐ΔPDF) method yields quantitative information on the distribution of defect layer spacings, which peaks at a value corresponding to Ge 3 Bi 2 Te 6 building blocks. The cation distribution along with the displacement of the atom layers is refined as well, using a least‐squares approach. Bi concentrates on cation positions next to the vacancy layers.