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Phys Rev Lett. 2009 Nov 6;103(19):195502. Epub 2009 Nov 6.

Nature of atomic bonding and atomic structure in the phase-change Ge2Sb2Te5 glass.

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Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.


Using electronic structure calculations, we demonstrate a global valence alternation in the amorphous Ge2Sb2Te5, a prototype phase-change alloy for data storage. The resulting p bonding profoundly influences the local atomic structure, leading to right-angle components similar to those in the crystalline counterpart of this chalcogenide glass. The dominance of p bonding is revealed by (i) distributions of the coordination number (CN) and the bond angle, for truly bonded atoms determined based on the electron localization function, and (ii) a direct evaluation of the p (and s) orbital occupation probability for the CN=3 Ge atoms that form 90 degree bonds with neighbors.

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