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@ARTICLE{Akola:59525,
      author       = {Akola, J. and Jones, R. O.},
      title        = {{S}tructural phase transitions on the nanoscale: {T}he
                      crucial pattern in the phase-change materials
                      {G}e2{S}b2{T}e5 and {G}e{T}e},
      journal      = {Physical review / B},
      volume       = {76},
      number       = {23},
      issn         = {1098-0121},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {PreJuSER-59525},
      pages        = {235201},
      year         = {2007},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {Phase-change materials are of immense importance for
                      optical recording and computer memory, but the structure of
                      the amorphous phases and the nature of the phase transition
                      in the nanoscale bits pose continuing challenges. Massively
                      parallel density functional simulations have been used to
                      characterize the amorphous structure of the prototype
                      materials Ge2Sb2Te5 and GeTe. In both, there is long-ranged
                      order among Te atoms and the crucial structural motif is a
                      four-membered ring with alternating atoms of types A (Ge and
                      Sb) and B (Te), an "ABAB square." The rapid
                      amorphous-to-crystalline phase change is a reorientation of
                      disordered ABAB squares to form an ordered lattice. There
                      are deviations from the "8-N rule" for coordination numbers,
                      with Te having near threefold coordination. Ge atoms are
                      predominantly fourfold coordinated, but-contrary to recent
                      speculation-tetrahedral coordination is found in only
                      approximately one-third of the Ge atoms. The average
                      coordination number of Sb atoms is 3.7, and the local
                      environment of Ge and Sb is usually "distorted octahedral"
                      with AB separations from 3.2 to 4 A in the first
                      coordination shell. The number of A-A bonds is significantly
                      greater in GeTe than in Ge2Sb2Te5. Vacancies (voids) in the
                      disordered phases of these materials provide the necessary
                      space for the phase transitions to take place. The vacancy
                      concentration in Ge2Sb2Te5 $(11.8\%)$ is greater than in
                      GeTe $(6.4\%),$ which is consistent with the better
                      phase-change performance of the former.},
      keywords     = {J (WoSType)},
      cin          = {IFF-1},
      ddc          = {530},
      cid          = {I:(DE-Juel1)VDB781},
      pnm          = {Kondensierte Materie},
      pid          = {G:(DE-Juel1)FUEK414},
      shelfmark    = {Physics, Condensed Matter},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000251986500054},
      doi          = {10.1103/PhysRevB.76.235201},
      url          = {https://juser.fz-juelich.de/record/59525},
}