Journal Article

PreJuSER-19977

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Hindered Rotational Energy Barriers of BH4- Tetrahedra in ß-Mg (BH4)2 from Quasielastic Neutron Scattering and DFT Calculations

Blanchard, D. ; Maronsson, J. B. ; Riktor, M. D. ; Kheres, J. ; Sveinbjörnsson, D. ; Bardají, E. G. ; Léon, A. ; Juranyi, F. ; Wuttke, J.FZJ* ; Lefmann, K. ; Hauback, B. C. ; Fichtner, M. ; Vegge, T.

2012
Soc. Washington, DC

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Please use a persistent id in citations: doi:10.1021/jp208670v

Abstract: In this work, hindered rotations of the BH4- tetrahedra in Mg(BH4)(2) were studied by quasielastic neutron scattering, using two instruments with different energy resolution, in combination with density functional theory (DFT) calculations. Two thermally activated reorientations of the BH4- units, around the 2-fold (C-2) and 3-fold (C-3) axes were observed at temperatures from 120 to 440 K. The experimentally obtained activation energies (E-aC2 = 39 and 76 meV and E-aC3 = 214 meV) and mean residence times between reorientational jumps are comparable with the energy barriers obtained from DFT calculations. A linear dependency of the energy barriers for rotations around the C-2 axis parallel to the Mg-Mg axis with the distance between these two axes was revealed by the DFT calculations. At the lowest temperature (120 K) only 15% of the BH4- units undergo rotational motion and from comparison with DFT results it is expectedly the BH4- units with the boron atom closest to the Mg-Mg axis, although dynamics related to local disorder existing at the boundary of the antiphase domains or to the presence of solvent in the sample cannot be strictly excluded. No long-range diffusion events were observed.

Keyword(s): Basic research (1st) ; Others (1st) ; Chemistry (2nd) ; J

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. It has been supported by the Danish Council for independent Research through DANSCATT. The authors 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 supercomputer 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.

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Contributing Institute(s):

1. Neutronenstreuung (ICS-1)
2. JCNS-FRM-II (JCNS (München) ; Jülich Centre for Neutron Science JCNS (München) ; JCNS-FRM-II)
3. Neutronenstreuung (JCNS-1)

Research Program(s):

1. BioSoft: Makromolekulare Systeme und biologische Informationsverarbeitung (P45)
2. Großgeräte für die Forschung mit Photonen, Neutronen und Ionen (PNI) (P55)

Experiment(s):

1. SPHERES: Backscattering spectrometer (NL6S)

Appears in the scientific report 2012

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Database coverage:
; Current Contents - Social and Behavioral Sciences ; JCR ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Thomson Reuters Master Journal List ; Web of Science Core Collection

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