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@ARTICLE{Blanchard:13318,
      author       = {Blanchard, D. and Riktor, M. and Maronsson, J. and
                      Jacobsen, H. and Kehres, J. and Sveinbjörnsson, D. and
                      Bardaji, E. and Léon, A. and Juranyi, F. and Wuttke, J. and
                      Hauback, B. and Fichtner, M. and Vegge, T.},
      title        = {{H}ydrogen {R}otational and {T}ranslational {D}iffusion in
                      {C}alcium {B}orohydride from {Q}uasielastic {N}eutron
                      {S}cattering and {DFT} {C}alculations},
      journal      = {The journal of physical chemistry / C},
      volume       = {114},
      issn         = {1932-7447},
      address      = {Washington, DC},
      publisher    = {Soc.},
      reportid     = {PreJuSER-13318},
      pages        = {20249 - 20257},
      year         = {2010},
      note         = {This work is based on experiments performed at the Swiss
                      spallation neutron source SINQ, Paul Scherrer Institute,
                      Villigen, Switzerland and at FRMII, JCNS Garching, Germany.
                      The authors would like to acknowledge the European Graduate
                      School for Sustainable Energy Technology and the Nordic
                      Center for Excellence on Hydrogen Storage Materials. The
                      Danish Center for Scientific Computing is acknowledged for
                      super-computer access. The Center for Atomic Materials
                      Design (CAMD) is supported by the Lundbeck Fondation.
                      Financial support by EU-IP NESSHY (Contract #518271) and the
                      ERA-NET project Hy-CO is also gratefully acknowledged.},
      abstract     = {Hydrogen dynamics in crystalline calcium borohydride can be
                      initiated by long-range diffusion or localized motion such
                      as rotations, librations, and vibrations. Herein, the
                      rotational and translational diffusion were studied by
                      quasielastic neutron scattering (QENS) by using two
                      instruments with different time scales in combination with
                      density functional theory (DFT) calculations. Two thermally
                      activated reorientational motions were observed, mound the
                      2-fold (C-2) and 3-fold (C-3) axes of the BH4- units, at
                      temperature from 95 to 280K. The experimental energy
                      barriers (Ea(C2) = 0.14 eV and Ea(C3) = 0.10 eV) and mean
                      residence times are comparable with those obtained from DFT
                      calculations. Long-range diffusion events, with an energy
                      barrier Of E-aD = 0.12 eV and an effective jump length of
                      similar to 2.5 angstrom were observed at 224 and 260 K.
                      Three vacancy-mediated diffusion events, H jumps between two
                      neighboring BH4-, and diffusion of BH4- and BH3 groups were
                      calculated and finally discarded because of their very high
                      formation energies and diffusion barriers. Three
                      interstitial diffusion processes (H, H-2, and H2O) were also
                      calculated. The H interstitial was found to be highly
                      unstable, whereas the H-2 interstitial has a low energy of
                      formation (0.40 eV) and diffusion barrier (0.09 eV) with a
                      jump length (2.1 angstrom) that corresponds well with the
                      experimental values. H2O interstitial has an energy of
                      formation of -0.05 eV, and two different diffusion pathways
                      were found. The first gives a H jump distance of 2.45
                      angstrom with a diffusion barrier of 0.68 eV, the second
                      one, more favorable, exhibits a H jump distance of 1.08
                      angstrom with a barrier of 0.40 eV. The correlation between
                      the QENS and DFT calculations indicates that, most probably,
                      it is the diffusion of interstitial H-2 that was observed.
                      The origin of the interstitial H-2 might come from the
                      synthesis of the compound or a side reaction with trapped
                      synthesis residue leading to the partial oxidation of the
                      compound and hydrogen release.},
      keywords     = {J (WoSType)},
      cin          = {IFF-4 / Jülich Centre for Neutron Science JCNS (JCNS) ;
                      JCNS},
      ddc          = {540},
      cid          = {I:(DE-Juel1)VDB784 / I:(DE-Juel1)JCNS-20121112},
      pnm          = {Großgeräte für die Forschung mit Photonen, Neutronen und
                      Ionen (PNI) / BioSoft: Makromolekulare Systeme und
                      biologische Informationsverarbeitung},
      pid          = {G:(DE-Juel1)FUEK415 / G:(DE-Juel1)FUEK505},
      experiment   = {EXP:(DE-MLZ)SPHERES-20140101},
      shelfmark    = {Chemistry, Physical / Nanoscience $\&$ Nanotechnology /
                      Materials Science, Multidisciplinary},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000284455200051},
      doi          = {10.1021/jp107281v},
      url          = {https://juser.fz-juelich.de/record/13318},
}