TY  - JOUR
AU  - Wei, Shuai
AU  - Persch, Christoph
AU  - Stolpe, Moritz
AU  - Evenson, Zach
AU  - Coleman, Garrett
AU  - Lucas, Pierre
AU  - Wuttig, Matthias
TI  - Violation of the Stokes–Einstein relation in Ge2Sb2Te5, GeTe, Ag4In3Sb67Te26, and Ge15Sb85, and its connection to fast crystallization
JO  - Acta materialia
VL  - 195
SN  - 1359-6454
CY  - Amsterdam [u.a.]
PB  - Elsevier Science
M1  - FZJ-2020-04764
SP  - 491 - 500
PY  - 2020
AB  - 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.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000552116400045
DO  - DOI:10.1016/j.actamat.2020.05.044
UR  - https://juser.fz-juelich.de/record/888210
ER  -