Journal Article

FZJ-2020-04764

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Violation of the Stokes–Einstein relation in Ge2Sb2Te5, GeTe, Ag4In3Sb67Te26, and Ge15Sb85, and its connection to fast crystallization

Wei, S. ; Persch, C. ; Stolpe, M. ; Evenson, Z. ; Coleman, G. ; Lucas, P. ; Wuttig, M. (Corresponding author)FZJ*

2020
Elsevier Science Amsterdam [u.a.]

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Please use a persistent id in citations: doi:10.1016/j.actamat.2020.05.044

Abstract: Phase-change materials (PCMs) are already commercialized in optical and non-volatile memory devices. Yet, the dynamics of atomic rearrangement processes and their temperature dependence, which govern their ultrafast switching, are still not fully understood. Here we use quasi-elastic neutron scattering to investigate the liquid-state dynamics of four prevailing PCMs Ge2Sb2Te5, GeTe, Ag4In3Sb67Te26(AIST), and Ge15Sb85 above their respective melting points Tm. Self-diffusion coefficients and structural relaxation times on the timescale of picoseconds are extracted from dynamic structure factors. The results indicate an unusual systematic violation of the Stokes-Einstein relation (SER) for each PCM in high-temperature regions above Tm, where the atomic-mobility is high. This is likely related to the formation of locally favored structures in liquid PCMs. Absolute values of diffusivity in the supercooled liquid AIST are derived from crystal-growth velocity, which are almost one order of magnitude higher than that expected from the SER in the technologically relevant temperature range ~20% below Tm. This is relevant to understand the crystallization kinetics of PCMs as crystal growth is controlled by diffusivity. Furthermore, the instantaneous shear modulus is determined ranging from 2 to 3 GPa for liquid PCMs, which permits extracting viscosity from microscopic structural relaxations usually accessible to simulations and scattering techniques.

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Contributing Institute(s):

1. JARA Institut Green IT (PGI-10)

Research Program(s):

1. 521 - Controlling Electron Charge-Based Phenomena (POF3-521) (POF3-521)

Appears in the scientific report 2020

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Engineering, Computing and Technology ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF >= 5 ; JCR ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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