Lattice disorder and oxygen migration pathways in pyrochlore and defect-fluorite oxides
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Date
2021-08-14
Journal Title
Journal ISSN
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Publisher
International Union of Crystallography
Abstract
Pyrochlore oxides, with the general formula A2B2O7, are of considerable interest as catalysts for the oxygen evolution reaction[1-5],
where A2Ru2O7-δ pyrochlores have recently emerged as state-of-the-art materials, and as photocatalysts for hydrogen evolution[6-8].
Fundamental to their reactivity is the local-scale vacancy ordering and mobility, which can be tailored through cation substitution[4].
The chemical and structural flexibility of pyrochlore oxides gives them a diverse range of physical and chemical properties leading to
technological applications including as fast-ion conductors[9, 10], ferroelectrics[11], magnetism[12], oxide heterostructures[13, 14],
and host matrices for the immobilization of actinide-rich nuclear wastes[15].
Atomic-scale disorder plays an important role in the chemical and physical properties of oxide materials. The structural flexibility of
pyrochlore-type oxides allows for crystal-chemical engineering of these properties. Compositional modification can push pyrochlore
oxides towards a disordered defect-fluorite structure with anion Frenkel pair defects that facilitate oxygen migration. The local
structure of the long-range average cubic defect-fluorite was recently claimed to consist of randomly arranged orthorhombic weberitetype
domains[16]. In this work we show, using low-temperature neutron total-scattering experiments, that this is not the case for Zrrich
defect-fluorites. By analyzing data from the pyrochlore/defect-fluorite Y2Sn2-xZrxO7 series using a combination of neutron pair
distribution function and big-box modelling, we have differentiated and quantified the relationship between anion sub-lattice disorder
and Frenkel defects. These details directly influence the energy landscape for oxygen migration and are crucial for simulations and
design of new materials with improved properties. © The Authors
Description
Keywords
Crystal defects, Pyrochlore, Fluorite, Order-disorder transformations, Crystal structure, Oxygen, Oxides
Citation
Marlton, F. P., Zhang, Z., Zhang, Y., Proffen, T. E., Ling, C. D., & Kennedy, B. J. (2021). Lattice disorder and oxygen migration pathways in pyrochlore and defect-fluorite oxides. Poster presented to the IUCr 2021, 25th Congress of the International Union of Crystallography, 14-22 August 2021, Prague, Czech Republic. In Acta Crystallographica Section A, 77(a2), C1083-C1084. doi:10.1107/S0108767321086190