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@ARTICLE{Wei:888210,
      author       = {Wei, Shuai and Persch, Christoph and Stolpe, Moritz and
                      Evenson, Zach and Coleman, Garrett and Lucas, Pierre and
                      Wuttig, Matthias},
      title        = {{V}iolation of the {S}tokes–{E}instein relation in
                      {G}e2{S}b2{T}e5, {G}e{T}e, {A}g4{I}n3{S}b67{T}e26, and
                      {G}e15{S}b85, and its connection to fast crystallization},
      journal      = {Acta materialia},
      volume       = {195},
      issn         = {1359-6454},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2020-04764},
      pages        = {491 - 500},
      year         = {2020},
      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.},
      cin          = {PGI-10},
      ddc          = {670},
      cid          = {I:(DE-Juel1)PGI-10-20170113},
      pnm          = {521 - Controlling Electron Charge-Based Phenomena
                      (POF3-521)},
      pid          = {G:(DE-HGF)POF3-521},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000552116400045},
      doi          = {10.1016/j.actamat.2020.05.044},
      url          = {https://juser.fz-juelich.de/record/888210},
}