title: The Crystal Structure of Ba3Nb2O8Revisited: A Neutron Diffraction and Solid-State NMR Study.
abstract: The structure of Ba3Nb2O8has been investigated using high resolution neutron powder diffraction. Our results show that, while the structure has some features in common with the 9R perovskite and palmierite structures, it is a new and distinct structure. It is shown to follow a (chh)(hhc)(chh) sequence with BaO3-δpacking layers and is a cation- and anion-deficient 9H perovskite polytype. Nb atoms occupy octahedral sites with vacancies between hexagonal close-packed layers. Isolated, corner-sharing and face-sharing Nb-O octahedra all occur within the unit cell. The identification of purely octahedral Nb is supported by solid-state93Nb wideline NMR measurements. A two-component line shape was detected: a narrow featureless resonance with an isotropic chemical shift of δiso-928 ± 5 ppm consistent with regular Nb octahedra, and a much broader featureless resonance with an approximate isotropic chemical shift in the range δiso∼ -944 to -937 ± 10 ppm consistent with Nb octahedra influenced by O vacancies. These are both characteristic of 6-fold oxo-coordinated Nb environments. The highly distorted octahedral environments in Ba3Nb2O8make it a potential candidate for dielectric and photocatalytic applications.
authors.affiliation: Department of Chemistry, School of Natural & Computing Sciences, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, U.K.
authors.forename: Eve J
authors.initials: EJ
authors.lastname: Wildman
authors.affiliation: Department of Chemistry, School of Natural & Computing Sciences, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, U.K.
authors.forename: Abbie C
authors.identifier: http://orcid.org/0000-0001-9960-723X
authors.initials: AC
authors.lastname: Mclaughlin
authors.affiliation: Department of Physics, University of Warwick , Gibbet Hill Rd., Coventry CV4 7AL, U.K.
authors.forename: James F
authors.initials: JF
authors.lastname: Macdonald
authors.affiliation: Department of Physics, University of Warwick , Gibbet Hill Rd., Coventry CV4 7AL, U.K.
authors.forename: John V
authors.initials: JV
authors.lastname: Hanna
authors.affiliation: Department of Chemistry, School of Natural & Computing Sciences, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, U.K.|Department of Physics, School of Natural & Computing Sciences, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, U.K.
authors.forename: Janet M S
authors.identifier: http://orcid.org/0000-0001-5249-5306
authors.initials: JM
authors.lastname: Skakle