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Durham University

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Publication details for Prof. Ivana Evans

Auckett, Josie E., Milton, Katherine L. & Evans, Ivana Radosavljevic (2019). Cation distributions and anion disorder in Ba3NbMO8.5 (M = Mo, W) materials: Implications for oxide ion conductivity. Chemistry of Materials 31(5): 1715-1719.

Author(s) from Durham

Abstract

Competitive oxide ion conductivity has been identified recently in members of the Ba3Nb1–y(Mo1–
xWx)1+yO8.5+½y (0 ≤ x ≤ 1, –0.3 ≤ y ≤ 0.2) series, which adopt a disordered rhombohedral “hybrid” structure combining
features of the 9R perovskite and palmierite structures. We report the first growth of Ba3NbMoO8.5 and Ba3NbWO8.5 single
crystals from molten phases and their characterisation using single-crystal x-ray diffraction data between 120 and 473 K.
Structure refinements reveal a previously unreported splitting of the central Nb/M cation site, rationalised by bonding
considerations, which imposes limitations on the material stoichiometry and possible arrangements of cations within the
face-sharing polyhedral stacks. Analysis of atomic displacement parameters and bond valence energy landscapes (BVELs)
gives new insight into the probable low-energy pathways for oxide ion diffusion in the hybrid structure, indicating that
they are three-dimensional and involve all crystallographically distinct oxygen sites. Evidence for considerable static
disorder of the oxide ions at temperatures below the onset of significant conductivity is also discussed.