The relationship between oxide-ion conductivity and cation vacancy order in the hybrid hexagonal perovskite Ba3VWO8.5

Asma Gilane, Sacha Fop, Falak Sher, Ronald I. Smith, Abbie C. McLaughlin* (Corresponding Author)

*Corresponding author for this work

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Abstract

Significant oxide ionic conductivity has recently been reported in cation-deficient hexagonal perovskite Ba3M’M’’O8.5 derivatives (M’ = Nb; M’’ = Mo, W), with disordered hybrid 9R-palmierite average structures. Here, we present a study of the crystal structure and electrical properties of the related compound Ba3VWO8.5. Electrical characterization demonstrates that Ba3VWO8.5 is also an oxide ion conductor with a bulk conductivity of 2.0 × 10-3 S cm-1 in air at 900 °C, thus revealing that it is possible to obtain oxide ion conducting Ba3M’M’’O8.5 materials with a variety of different M’M’’ combinations. Whilst Ba3NbMoO8.5 and Ba3NbWO8.5 present a random distribution of cationic vacancies, X-ray and neutron diffraction experiments demonstrate that the cationic vacancies are ordered on the M2 sites in Ba3VWO8.5, resulting in a structure where M1Ox palmierite-like layers are separated by empty octahedral cavities. Bond-valence site energy (BVSE) analysis on the different phases reveals that ordering of the cationic vacancies hinders long-range oxygen diffusivity parallel to the c-axis in Ba3VWO8.5 explaining the reduced ionic conductivity of this compound. These results suggest that, together with the dominant 2-dimensional conduction pathway along the palmierite-like layers, additional diffusion routes parallel to the c-axis provide a relevant contribution to the conductivity of these Ba3M’M’’O8.5 systems by creation of a complex 3-dimensional ionic percolation network, the topology of which depends on the particular arrangement of cation and anion vacancies.
Original languageEnglish
Pages (from-to)16506-16514
Number of pages9
JournalJournal of Materials Chemistry A
Volume8
Issue number32
Early online date22 Jul 2020
DOIs
Publication statusPublished - 28 Aug 2020

Bibliographical note

Open Access via the Jisc RSC Agreement
Acknowledgements
We thank the UK Science and Technology Facilities Council (STFC) for provision of Xpress Access neutron beamtime at ISIS. This research was supported by the Leverhulme trust (RPG-2017-351) and the Commonwealth Scholarship Commission for provision of a split-site studentship for AG.

Keywords

  • CRYSTAL-STRUCTURE
  • TEMPERATURE
  • TRANSITION
  • CONDUCTORS
  • TRANSPORT
  • COORDINATION
  • DISTORTIONS
  • DIFFUSION
  • MIGRATION
  • STACKING

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