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@ARTICLE{Schie:829958,
      author       = {Schie, Marcel and Müller, Michael P. and Salinga, Martin
                      and Waser, R. and De Souza, Roger A.},
      title        = {{I}on migration in crystalline and amorphous
                      {H}f{O}$_{{X}}$},
      journal      = {The journal of chemical physics},
      volume       = {146},
      number       = {9},
      issn         = {1089-7690},
      address      = {Melville, NY},
      publisher    = {American Institute of Physics},
      reportid     = {FZJ-2017-03562},
      pages        = {094508 -},
      year         = {2017},
      abstract     = {The migration of ions in HfOx was investigated by means of
                      large-scale, classical molecular-dynamics simulations over
                      the temperature range 1000≤T/K≤2000. Amorphous HfOx was
                      studied in both stoichiometric and oxygen-deficient forms
                      (i.e., with x = 2 and x = 1.9875); oxygen-deficient cubic
                      and monoclinic phases were also studied. The mean square
                      displacement of oxygen ions was found to evolve linearly as
                      a function of time for the crystalline phases, as expected,
                      but displayed significant negative deviations from linear
                      behavior for the amorphous phases, that is, the behavior was
                      sub-diffusive. That oxygen-ion migration was observed for
                      the stoichiometric amorphous phase argues strongly against
                      applying the traditional model of vacancy-mediated migration
                      in crystals to amorphous HfO2. In addition, cation
                      migration, whilst not observed for the crystalline phases
                      (as no cation defects were present), was observed for both
                      amorphous phases. In order to obtain activation enthalpies
                      of migration, the residence times of the migrating ions were
                      analyzed. The analysis reveals four activation enthalpies
                      for the two amorphous phases: 0.29 eV, 0.46 eV, and 0.66 eV
                      (values very close to those obtained for the monoclinic
                      structure) plus a higher enthalpy of at least 0.85 eV. In
                      comparison, the cubic phase is characterized by a single
                      value of 0.43 eV. Simple kinetic Monte Carlo simulations
                      suggest that the sub-diffusive behavior arises from
                      nanoscale confinement of the migrating ions.},
      cin          = {PGI-7 / JARA-FIT / JARA-HPC},
      ddc          = {540},
      cid          = {I:(DE-Juel1)PGI-7-20110106 / $I:(DE-82)080009_20140620$ /
                      $I:(DE-82)080012_20140620$},
      pnm          = {521 - Controlling Electron Charge-Based Phenomena
                      (POF3-521) / Modelling the Valency Change Memory Effect in
                      Resistive Switching Random Access Memory (RRAM)
                      $(jpgi70_20120501)$},
      pid          = {G:(DE-HGF)POF3-521 / $G:(DE-Juel1)jpgi70_20120501$},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000397312800060},
      doi          = {10.1063/1.4977453},
      url          = {https://juser.fz-juelich.de/record/829958},
}