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@ARTICLE{Ceretti:276650,
      author       = {Ceretti, M. and Wahyudi, O. and Cousson, A. and
                      Villesuzanne, A. and Meven, M. and Pedersen, B. and Bassat,
                      J. M. and Paulus, W.},
      title        = {{L}ow temperature oxygen diffusion mechanisms in {N}d
                      $_{2}$ {N}i{O} $_{4+δ}$ and {P}r $_{2}$ {N}i{O} $_{4+δ}$
                      via large anharmonic displacements, explored by single
                      crystal neutron diffraction},
      journal      = {Journal of materials chemistry / A},
      volume       = {3},
      number       = {42},
      issn         = {2050-7496},
      address      = {London {[u.a.]},
      publisher    = {RSC},
      reportid     = {FZJ-2015-06978},
      pages        = {21140 - 21148},
      year         = {2015},
      abstract     = {We investigated the structure of Nd2NiO4+δ and Pr2NiO4+δ
                      by single crystal neutron diffraction studies. While the
                      real structure of both compounds is incommensurate, the
                      scattering density of the respective average structures was
                      explored using the Maximum Entropy Method. Unusually high
                      displacement factors were found for the equatorial and
                      apical oxygen atoms showing respectively large displacement
                      amplitudes towards [001] and [110] with respect to the
                      F-symmetry cell. The shifts of the apical oxygen atoms reach
                      up to 1 Å from their average position, corresponding to a
                      25° tilt of the NiO6 octahedra. At 400 °C, i.e. slightly
                      above the orthorhombic-tetragonal phase transition, the
                      anharmonic apical oxygen displacements towards [110] in the
                      commensurate tetragonal parent structure are strongly
                      enhanced, showing a double-well potential and pointing
                      towards the interstitial vacancy sites, creating a quasi
                      continuous shallow energy diffusion pathway between apical
                      and interstitial oxygen sites. These large displacement
                      amplitudes are considered to be – at least partially –
                      of dynamical origin, which is consistent with a phonon
                      assisted diffusion mechanism, already activated at very
                      moderate temperatures.},
      cin          = {JCNS (München) ; Jülich Centre for Neutron Science JCNS
                      (München) ; JCNS-FRM-II / JCNS-2},
      ddc          = {540},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-2-20110106},
      pnm          = {6G15 - FRM II / MLZ (POF3-6G15) / 6G4 - Jülich Centre for
                      Neutron Research (JCNS) (POF3-623)},
      pid          = {G:(DE-HGF)POF3-6G15 / G:(DE-HGF)POF3-6G4},
      experiment   = {EXP:(DE-MLZ)HEIDI-20140101 / EXP:(DE-MLZ)RESI-20140101},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000363163200037},
      doi          = {10.1039/C5TA05767A},
      url          = {https://juser.fz-juelich.de/record/276650},
}