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Average and Local Structure of Apatite-Type Germanates and Implications for Oxide Ion Conductivity

Chambers, Matthew S.; Chater, Philip A.; Evans, Ivana Radosavljevic; Evans, John S.O.

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Authors

Matthew S. Chambers

Philip A. Chater

Ivana Radosavljevic Evans



Contributors

Abstract

Materials with the apatite structure have a range of important applications in which their function is influenced by details of their local structure. Here, we describe an average and local structural study to probe the origins of high-temperature oxide ion mobility in La10(GeO4)6O3 and La8Bi2(GeO4)6O3 oxygen-excess materials, using the low-conductivity interstitial oxide-free La8Sr2(GeO4)6O2 as a benchmark. For La10 and La8Bi2, we locate the interstitial oxygen, Oint, responsible for conductivity by Rietveld refinement and relate the P63/m to P1̅ phase transitions on cooling to oxygen ordering. Local structural studies using neutron total scattering reveal that well-ordered GeO5 square pyramidal groups form in the structure at low temperature, but that Oint becomes significantly more disordered in the high-conductivity, high-temperature structures, with a transition to more trigonal-bipyramid-like average geometry. We relate the higher conductivity of Bi materials to the presence of several Oint sites of similar energy in the structure, which correlates with its less-distorted low-temperature average structure.

Citation

Chambers, M. S., Chater, P. A., Evans, I. R., & Evans, J. S. (2019). Average and Local Structure of Apatite-Type Germanates and Implications for Oxide Ion Conductivity. Inorganic Chemistry, 58(21), 14853-14862. https://doi.org/10.1021/acs.inorgchem.9b02544

Journal Article Type Article
Online Publication Date Oct 16, 2019
Publication Date Nov 4, 2019
Deposit Date Nov 5, 2019
Publicly Available Date Oct 16, 2020
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 58
Issue 21
Article Number 14853-14862
Pages 14853-14862
DOI https://doi.org/10.1021/acs.inorgchem.9b02544

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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.9b02544





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