Structure determination of Ba 5 AlF 13 by coupling electron, synchrotron and neutron powder diffraction, solid-state NMR and ab initio calculations

Abstract : The room temperature structure of Ba 5 AlF 13 has been investigated by coupling electron, synchrotron and neutron powder diffraction, solid-state high-resolution NMR (19 F and 27 Al) and first principles calculations. An initial structural model has been obtained from electron and synchrotron powder diffraction data, and its main features have been confirmed by one-and two-dimensional NMR measurements. However, DFT GIPAW calculations of the 19 F isotropic shieldings revealed an inaccurate location of one fluorine site (F3, site 8a), which exhibited unusual long F–Ba distances. The atomic arrangement was reinvestigated using neutron powder diffraction data. Subsequent Fourier maps showed that this fluorine atom occupies a crystallographic site of lower symmetry (32e) with partial occupancy (25%). GIPAW computations of the NMR parameters validate the refined structural model, ruling out the presence of local static disorder and indicating that the partial occupancy of this F site reflects a local motional process. Visualisation of the dynamic process was then obtained from the Rietveld refinement of neutron diffraction data using an anharmonic description of the displacement parameters to account for the thermal motion of the mobile fluorine. The whole ensemble of powder diffraction and NMR data, coupled with first principles calculations , allowed drawing an accurate structural model of Ba 5 AlF 13 , including site-specific dynamical disorder in the fluorine sub-network.
Type de document :
Article dans une revue
Dalton Transactions, Royal Society of Chemistry, 2016, 45, pp.15565. <10.1039/c6dt02454h>
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https://hal.archives-ouvertes.fr/hal-01391171
Contributeur : Dominique Massiot <>
Soumis le : mercredi 2 novembre 2016 - 23:13:18
Dernière modification le : samedi 18 février 2017 - 01:16:11

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Charlotte Martineau, Mathieu Allix, Matthew Suchomel, Florence Porcher, François Vivet, et al.. Structure determination of Ba 5 AlF 13 by coupling electron, synchrotron and neutron powder diffraction, solid-state NMR and ab initio calculations. Dalton Transactions, Royal Society of Chemistry, 2016, 45, pp.15565. <10.1039/c6dt02454h>. <hal-01391171>

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