Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material.
AffiliationUniv Arizona, Dept Mat Sci & Engn
MetadataShow full item record
PublisherAMER ASSOC ADVANCEMENT SCIENCE
CitationWei, S., Evenson, Z., Stolpe, M., Lucas, P., & Angell, C. A. (2018). Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material. Science advances, 4(11), eaat8632.
RightsCopyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
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AbstractThe dynamic properties of liquid phase-change materials (PCMs), such as viscosity η and the atomic self-diffusion coefficient D, play an essential role in the ultrafast phase switching behavior of novel nonvolatile phase-change memory applications. To connect η to D, the Stokes-Einstein relation (SER) is commonly assumed to be valid at high temperatures near or above the melting temperature Tm and is often used for assessing liquid fragility (or crystal growth velocity) of technologically important PCMs. However, using quasi-elastic neutron scattering, we provide experimental evidence for a breakdown of the SER even at temperatures above Tm in the high-atomic mobility state of a PCM, Ge1Sb2Te4. This implies that although viscosity may have strongly increased during cooling, diffusivity can remain high owing to early decoupling, being a favorable feature for the fast phase switching behavior of the high-fluidity PCM. We discuss the origin of the observation and propose the possible connection to a metal-semiconductor and fragile-strong transition hidden below Tm.
NoteOpen access journal
VersionFinal published version
SponsorsFRM II; Feodor Lynen Postdoctoral Research Fellowship of the Alexander von Humboldt Foundation; Place-to-be RWTH Start-Up fund; DFG [SFB917]; NSF-EFRI award ; National Science Foundation Research [CHE-1213265]