Issue 32, 2020

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

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.

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

Supplementary files

Article information

Article type
Paper
Submitted
03 Jūn. 2020
Accepted
21 Jūl. 2020
First published
22 Jūl. 2020
This article is Open Access
Creative Commons BY-NC license

J. Mater. Chem. A, 2020,8, 16506-16514

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

A. Gilane, S. Fop, F. Sher, R. I. Smith and A. C. Mclaughlin, J. Mater. Chem. A, 2020, 8, 16506 DOI: 10.1039/D0TA05581F

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