Emerging Anion Disorder in CaTi<inf>1-x</inf>Fe<inf>x</inf>O<inf>3-x/2</inf> Perovskites by X-ray Spectroscopy and Neutron Total Scattering
- Publisher:
- AMER CHEMICAL SOC
- Publication Type:
- Journal Article
- Citation:
- Chemistry of Materials, 2024, 36, (18), pp. 8811-8824
- Issue Date:
- 2024-01-01
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| mullens-et-al-2024-emerging-anion-disorder-in-cati1-xfexo3-x-2-perovskites-by-x-ray-spectroscopy-and-neutron-total.pdf | Published version | 7.07 MB |
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The long-range average and short-range local structures of the perovskite-type CaTi1-xFexO3-x/2 (0.00 ≤ x ≤ 0.40) oxides have been determined using high-resolution synchrotron X-ray diffraction (SXRD), neutron powder diffraction (NPD), and neutron pair distribution function (NPDF) methods, supported by X-ray absorption near-edge structure spectroscopy (XANES). Partial replacement of Ti4+ by Fe3+ leads to an increase in symmetry in the long-range average structure from orthorhombic Pbnm to cubic Pm3̅m. This also leads to the introduction of anion vacancies with disordering of the anion sublattice observed as broad and diffuse reflections in the NPD. Changes in the Fe L3-edge features upon doping demonstrate a significant change in the Fe3+ coordination environment. However, only subtle changes are observed in the Ti L3-edge spectra, suggesting that the oxygen vacancies are predominantly located around the Fe3+ cations. The NPDF analysis confirms that the anion vacancies sit preferentially around the Fe3+ cations, resulting in the formation of a range of differently sized FeOn (n = 4, 5, 6) polyhedra and disordered polyhedral tilting. The change from a long-range orthorhombic Pbnm to a cubic Pm3̅m structure is strongly correlated with a change in the Ca2+ off-centering and displacement. We relate our findings to the previously reported ionic conductivities of these compositions for a complete structure-property relationship. This work has revealed local and engineerable structural complexities beyond the average structure and improves our understanding of the structure-property relationships of perovskites for application in solid-state ionic conductors and oxygen-transport membranes.
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