Expanded chemistry and mixed ionic-electronic conductivity in vanadium-substituted variants of γ-Ba4Nb2O9
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Date
2021-08-14
Journal Title
Journal ISSN
Volume Title
Publisher
International Union of Crystallography
Abstract
Two new compositional series with the previously unique γ-Ba4Nb2O9 type structure, γ-Ba4VxTa2-xO9 and γ-Ba4VxNb2-xO9 (x = 0-2/3), have been synthesised via solid-state methods. Undoped Ba4Ta2O9 forms a 6H-perovskite type phase, but with sufficient V doping the γ-type phase is thermodynamically preferred and possibly more stable than γ-Ba4Nb2O9, forming at a 200 °C lower synthesis temperature. This is explained by the fact that Nb5+ ions in γ-Ba4Nb2O9 simultaneously occupy 4-, 5- and 6-coordinate sites in the oxide sublattice, which is less stable than allowing smaller V5+ to occupy the former and larger Ta5+ to occupy the latter. We characterised the structures of the new phases using a combination of X-ray and neutron powder diffraction. All compositions hydrate rapidly and extensively (up to 1/3 H2O per formula unit) under ambient conditions, like the parent γ-Ba4Nb2O9 phase, and show moderate but improved mixed-ionic electronic conduction. At lower temperatures the ionic conduction is predominately protonic, while at higher temperatures it is dominated by oxide and electron-hole conduction.
Description
Keywords
X-ray diffraction, Electric conductivity, Thermal gravimetric analysis, Neutron diffraction, Perovskite, Proton conductivity, Hydration, Vanadium, Ionic conductivity
Citation
Brown, A., Schwaighofer, B., Avdeev, M., Johannessen, B., Radosavljevic-Evans, I., & Ling, C. (2021). Expanded chemistry and mixed ionic-electronic conductivity in vanadium-substituted variants of [gamma]-Ba4Nb2O9. Poster presented to IUCr 2021, 25th Congress of the International Union of Crystallography, Prague, Czech Republic, 14-22 August 2021. In Acta Crystallographica Section A, 77(a2), C1080. doi:10.1107/S0108767321086220