title: Structure determination of Ba5AlF13by coupling electron, synchrotron and neutron powder diffraction, solid-state NMR and ab initio calculations.
abstract: The room temperature structure of Ba5AlF13has been investigated by coupling electron, synchrotron and neutron powder diffraction, solid-state high-resolution NMR (19F and27Al) 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 the19F 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 Ba5AlF13, including site-specific dynamical disorder in the fluorine sub-network.
authors.affiliation: Tectospin, Institut Lavoisier de Versailles, CNRS UMR 8180, Université de Versailles Saint-Quentin en Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles Cedex, France. charlotte.martineau@uvsq.fr francis.taulelle@chimie.uvsq.fr and CNRS, CEMHTI UPR3079, Université d'Orléans, F-45071 Orléans, France. mathieu.allix@cnrs-orleans.fr dominique.massiot@cnrs-orleans.fr franck.fayon@cnrs-orleans.fr.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Martineau
authors.affiliation: CNRS, CEMHTI UPR3079, Université d'Orléans, F-45071 Orléans, France. mathieu.allix@cnrs-orleans.fr dominique.massiot@cnrs-orleans.fr franck.fayon@cnrs-orleans.fr.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Allix
authors.affiliation: Argonne National Laboratory, Advanced Photon Source, Argonne, IL 60439, USA. Matthew.Suchomel@icmcb.cnrs.fr.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Suchomel
authors.affiliation: CEA Saclay, Laboratoire Léon Brillouin, 91191 Gif sur Yvette, France. florence.porcher@cea.fr.
authors.forename: Florence
authors.initials: F
authors.lastname: Porcher
authors.affiliation: CNRS, CEMHTI UPR3079, Université d'Orléans, F-45071 Orléans, France. mathieu.allix@cnrs-orleans.fr dominique.massiot@cnrs-orleans.fr franck.fayon@cnrs-orleans.fr.
authors.forename: François
authors.initials: F
authors.lastname: Vivet
authors.affiliation: Université Bretagne Loire, Université du Maine, CNRS UMR 6283, Institut des Molécules et des Matériaux du Mans, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France. christophe.legein@univ-lemans.fr monique.body@univ-lemans.fr.
authors.forename: Christophe
authors.identifier: http://orcid.org/0000-0001-7426-8817
authors.initials: C
authors.lastname: Legein
authors.affiliation: Université Bretagne Loire, Université du Maine, CNRS UMR 6283, Institut des Molécules et des Matériaux du Mans, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France. christophe.legein@univ-lemans.fr monique.body@univ-lemans.fr.
authors.forename: Monique
authors.initials: M
authors.lastname: Body
authors.affiliation: CNRS, CEMHTI UPR3079, Université d'Orléans, F-45071 Orléans, France. mathieu.allix@cnrs-orleans.fr dominique.massiot@cnrs-orleans.fr franck.fayon@cnrs-orleans.fr.
authors.forename: Dominique
authors.initials: D
authors.lastname: Massiot
authors.affiliation: Tectospin, Institut Lavoisier de Versailles, CNRS UMR 8180, Université de Versailles Saint-Quentin en Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles Cedex, France. charlotte.martineau@uvsq.fr francis.taulelle@chimie.uvsq.fr.
authors.forename: Francis
authors.initials: F
authors.lastname: Taulelle
authors.affiliation: CNRS, CEMHTI UPR3079, Université d'Orléans, F-45071 Orléans, France. mathieu.allix@cnrs-orleans.fr dominique.massiot@cnrs-orleans.fr franck.fayon@cnrs-orleans.fr.
authors.forename: Franck
authors.initials: F
authors.lastname: Fayon