The Crystal Structure of Ba3Nb2O8 Revisited: A Neutron Diffraction and Solid-State NMR Study

Eve J. Wildman, Abbie C. McLaughlin, James F MacDonald, John V Hanna, Janet M S Skakle

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Abstract

The structure of Ba3Nb2O8 has been investigated using high resolution neutron powder diffraction. Our results show that whilst 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-packing layers and is a cation and aniondeficient 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 state 93Nb 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 - –937 ± 10 ppm consistent with Nb octahedra influenced by O vacancies. These are both characteristic of six-fold oxo-coordinated Nb environments. The highly distorted octahedral environments in Ba3Nb2O8 make it a potential candidate for dielectric and photocatalytic applications.
Original languageEnglish
Pages (from-to)2653-2661
Number of pages9
JournalInorganic Chemistry
Volume56
Issue number5
Early online date10 Feb 2017
DOIs
Publication statusPublished - 2017

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Chemical shift
Neutron diffraction
Vacancies
chemical equilibrium
neutron diffraction
Crystal structure
Nuclear magnetic resonance
solid state
nuclear magnetic resonance
crystal structure
Neutron powder diffraction
line shape
Cations
cations
neutrons
Atoms
high resolution
cells
diffraction
atoms

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The Crystal Structure of Ba3Nb2O8 Revisited : A Neutron Diffraction and Solid-State NMR Study. / Wildman, Eve J.; McLaughlin, Abbie C.; MacDonald, James F; Hanna, John V; Skakle, Janet M S.

In: Inorganic Chemistry, Vol. 56, No. 5, 2017, p. 2653-2661.

Research output: Contribution to journalArticle

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abstract = "The structure of Ba3Nb2O8 has been investigated using high resolution neutron powder diffraction. Our results show that whilst 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-packing layers and is a cation and aniondeficient 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 state 93Nb 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 - –937 ± 10 ppm consistent with Nb octahedra influenced by O vacancies. These are both characteristic of six-fold oxo-coordinated Nb environments. The highly distorted octahedral environments in Ba3Nb2O8 make it a potential candidate for dielectric and photocatalytic applications.",
author = "Wildman, {Eve J.} and McLaughlin, {Abbie C.} and MacDonald, {James F} and Hanna, {John V} and Skakle, {Janet M S}",
note = "JMSS, ACM and EJW acknowledge support from the University of Aberdeen for funding and RCUK/ISIS for neutron time. JVH acknowledges the continued funding of the Solid State NMR Facility and other instrumentation at Warwick used in this research which was facilitated by EPSRC, the University of Warwick and partial funding through Birmingham Science City Advanced Materials Projects 1 and 2, which in turn was supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF).",
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AU - MacDonald, James F

AU - Hanna, John V

AU - Skakle, Janet M S

N1 - JMSS, ACM and EJW acknowledge support from the University of Aberdeen for funding and RCUK/ISIS for neutron time. JVH acknowledges the continued funding of the Solid State NMR Facility and other instrumentation at Warwick used in this research which was facilitated by EPSRC, the University of Warwick and partial funding through Birmingham Science City Advanced Materials Projects 1 and 2, which in turn was supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF).

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N2 - The structure of Ba3Nb2O8 has been investigated using high resolution neutron powder diffraction. Our results show that whilst 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-packing layers and is a cation and aniondeficient 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 state 93Nb 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 - –937 ± 10 ppm consistent with Nb octahedra influenced by O vacancies. These are both characteristic of six-fold oxo-coordinated Nb environments. The highly distorted octahedral environments in Ba3Nb2O8 make it a potential candidate for dielectric and photocatalytic applications.

AB - The structure of Ba3Nb2O8 has been investigated using high resolution neutron powder diffraction. Our results show that whilst 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-packing layers and is a cation and aniondeficient 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 state 93Nb 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 - –937 ± 10 ppm consistent with Nb octahedra influenced by O vacancies. These are both characteristic of six-fold oxo-coordinated Nb environments. The highly distorted octahedral environments in Ba3Nb2O8 make it a potential candidate for dielectric and photocatalytic applications.

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