Journal Article

PreJuSER-14666

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Polymorphism in phase-change materials: melt-quenched and as-deposited amorphous structures in Ge_2 Sb_2 Te_5 from density functional calculations

Akola, J. ; Larrucea, J. ; Jones, R. O.FZJ*

2011
APS College Park, Md.

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Please use a persistent id in citations: http://hdl.handle.net/2128/10942  doi:10.1103/PhysRevB.83.094113

Abstract: The as-deposited (AD) amorphous structure of the prototype phase change material Ge2Sb2Te5 (GST-225) has been studied by density functional calculations for a 648-atom sample generated by computer-aided deposition at 300 K. The AD sample differs from a melt-quenched (MQ) sample in essential ways: (1) Ge atoms are predominantly tetrahedrally coordinated, and (2) homopolar and Ge-Sb bonds are more common and reduce the number of ABAB squares (A = Ge, Sb; B = Te), the characteristic building blocks of the material. The first observation resolves the contradiction between measured (EXAFS) and calculated Ge-Te bond lengths, and the latter explains the very different crystallization speeds. Sb and Te have higher chemical coordination than suggested by the "8-N rule" of covalent networks (N is the number of valence electrons). The EXAFS signal calculated for AD agrees much better with experiment than that calculated for MQ.

Keyword(s): J

Note: The calculations were performed on the Jugene (IBM Blue Gene/P) and Juropa (Intel Xeon 5570) computers in the FZ Julich with grants from the FZJ and the John von Neumann Institute for Computing (NIC). We thank A. Filipponi for calculating EXAFS from our partial PDF, S. Kohara, T. Matsunaga, and N. Yamada for discussions and support, and the Academy of Finland for funding.

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Contributing Institute(s):

1. Quanten-Theorie der Materialien (PGI-1)

Research Program(s):

1. Grundlagen für zukünftige Informationstechnologien (P42)

Appears in the scientific report 2011

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