Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material
Open Access
- 2 November 2018
- journal article
- research article
- Published by American Association for the Advancement of Science (AAAS) in Science Advances
- Vol. 4 (11), eaat8632
- https://doi.org/10.1126/sciadv.aat8632
Abstract
The 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.Keywords
Funding Information
- National Science Foundation (1640860)
- National Science Foundation (CHE-1213265)
- Alexander von Humboldt-Stiftung (Feoder-Lynen Research Fellowship)
- RWTH Aachen University (Place-to-be RWTH Start-Up)
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