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Synthesis, structural characterisation and proton conduction of two new hydrated phases of barium ferrite BaFeO2.5−x(OH)2x

Knöchel, Patrick L. and Keenan, Philip J. and Loho, Christoph and Reitz, Christian and Witte, Ralf and Knight, Kevin S. and Wright, Adrian J. and Hahn, Horst and Slater, Peter R. and Clemens, Oliver (2016):
Synthesis, structural characterisation and proton conduction of two new hydrated phases of barium ferrite BaFeO2.5−x(OH)2x.
In: Journal of Materials Chemistry A, 4 (9), pp. 3415-3430. Royal Society of Chemistry, ISSN 2050-7488,
DOI: 10.1039/c5ta06383c,
[Article]

Abstract

Materials exhibiting mixed electronic and proton conductivity are of great interest for applications ranging from electrodes for proton conducting ceramic fuel cells to hydrogen separation membranes. In this work, we report a detailed investigation of the effect of water incorporation in BaFeO2.5 on the structure and conductivity. BaFeO2.5 is shown to be topochemically transformed to two different hydrated modifications, low-water (LW-) and high-water (HW-) BaFeO2.5. A combined analysis of neutron and X-ray diffraction data was used to determine the crystal structure of LW-BaFeO2.5 (BaFeO2.33(OH)0.33), which shows a unique ordering pattern of anion vacancies for perovskite type compounds, with structural relaxations around vacancies being similar to the chemically similar compound BaFeO2.33F0.33. Approximate proton positions were determined using the bond valence method. Conductivity studies of hydrated and pure BaFeO2.5 (with additional comparison to oxidized BaFeO2.5) show a significant enhancement of the conductivity on water incorporation, which can be attributed to proton conductivity. This is the first report of significant grain proton conduction (∼10−6 to 10−7 S cm−1) in an iron based perovskite. Water uptake is further shown to be completely reversible, with reformation of BaFeO2.5 when heating the compound to temperatures above ∼450 K under Ar.

Item Type: Article
Erschienen: 2016
Creators: Knöchel, Patrick L. and Keenan, Philip J. and Loho, Christoph and Reitz, Christian and Witte, Ralf and Knight, Kevin S. and Wright, Adrian J. and Hahn, Horst and Slater, Peter R. and Clemens, Oliver
Title: Synthesis, structural characterisation and proton conduction of two new hydrated phases of barium ferrite BaFeO2.5−x(OH)2x
Language: English
Abstract:

Materials exhibiting mixed electronic and proton conductivity are of great interest for applications ranging from electrodes for proton conducting ceramic fuel cells to hydrogen separation membranes. In this work, we report a detailed investigation of the effect of water incorporation in BaFeO2.5 on the structure and conductivity. BaFeO2.5 is shown to be topochemically transformed to two different hydrated modifications, low-water (LW-) and high-water (HW-) BaFeO2.5. A combined analysis of neutron and X-ray diffraction data was used to determine the crystal structure of LW-BaFeO2.5 (BaFeO2.33(OH)0.33), which shows a unique ordering pattern of anion vacancies for perovskite type compounds, with structural relaxations around vacancies being similar to the chemically similar compound BaFeO2.33F0.33. Approximate proton positions were determined using the bond valence method. Conductivity studies of hydrated and pure BaFeO2.5 (with additional comparison to oxidized BaFeO2.5) show a significant enhancement of the conductivity on water incorporation, which can be attributed to proton conductivity. This is the first report of significant grain proton conduction (∼10−6 to 10−7 S cm−1) in an iron based perovskite. Water uptake is further shown to be completely reversible, with reformation of BaFeO2.5 when heating the compound to temperatures above ∼450 K under Ar.

Journal or Publication Title: Journal of Materials Chemistry A
Journal volume: 4
Number: 9
Publisher: Royal Society of Chemistry
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Fachgebiet Materialdesign durch Synthese
11 Department of Materials and Earth Sciences > Material Science > Joint Research Laboratory Nanomaterials
Date Deposited: 22 Mar 2017 11:10
DOI: 10.1039/c5ta06383c
Official URL: https://doi.org/10.1039/c5ta06383c
Funders: Neutron diffraction beam time at ISIS was provided by the Science and Technology Facilities Council (STFC).
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