Simulation of Crystallization in Ge[subscript 2]Sb[subscript 2]Te[subscript 2]: A Memory Effect in the Canonical Phase-Change Material
Name
PhysRevB.90.184109.pdf
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2.93 MB
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Adobe PDF
Checksum (MD5)
7391a1dc902de8d951b00b0e2a6e3571
Author(s)
Akola, J.
Jones, R. O.
Kalikka, Janne
Date Issued
November 2014
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
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.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
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DOI of Published Version
https://doi.org/10.1103/PhysRevB.90.184109
