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Simulation of Crystallization in Ge[subscript 2]Sb[subscript 2]Te[subscript 2]: A Memory Effect in the Canonical Phase-Change Material

Author(s)
Akola, J.; Jones, R. O.; Kalikka, Janne
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Abstract
Crystallization of amorphous Ge[subscript 2]Sb[subscript 2]Te[subscript 5] (GST) has been studied using four extensive (460 atoms, up to 4 ns) density functional/molecular dynamics simulations at 600 K. This phase change material is a rare system where crystallization can be simulated without adjustable parameters over the physical time scale, and the results could provide insight into order-disorder processes in general. Crystallization is accompanied by an increase in the number of ABAB squares (A : Ge,Sb; B : Te), percolation, and the occurrence of low-frequency localized vibration modes. A sample with a history of order crystallizes completely in 1.2 ns, but ordering in others was less complete, even after 4 ns. The amorphous starting structures without memory display phases (>1ns) with subcritical nuclei (10–50 atoms) ranging from nearly cubical blocks to stringlike configurations of ABAB squares and AB bonds extending across the cell. Percolation initiates the rapid phase of crystallization and is coupled to the directional p-type bonding in metastable GST. Cavities play a crucial role, and the final ordered structure is distorted rock salt with a face-centered cubic sublattice containing predominantly Te atoms. We comment on earlier models based on smaller and much shorter simulations.
Date issued
2014-11
URI
http://hdl.handle.net/1721.1/92241
Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Journal
Physical Review B
Publisher
American Physical Society
Citation
Kalikka, J., J. Akola, and R. O. Jones. “Simulation of Crystallization in Ge[subscript 2]Sb[subscript 2]Te[subscript 2]: A Memory Effect in the Canonical Phase-Change Material.” Physical Review B 90.18 (2014): n. pag. © 2014 American Physical Society
Version: Final published version
ISSN
1098-0121
1550-235X

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