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Emerging Anion Disorder in CaTi1–xFexO3–x/2 Perovskites by X-ray Spectroscopy and Neutron Total Scattering
Chemistry of Materials ( IF 7.2 ) Pub Date : 2024-09-11 , DOI: 10.1021/acs.chemmater.4c01590
Bryce G. Mullens 1 , Frederick P. Marlton 1, 2 , Matilde Saura-Múzquiz 1, 3 , Maria K. Nicholas 1 , Ahmadi J. Permana 1, 4 , Bruce C. Cowie 5 , Valerie Mitchell 5 , Cheng Li 6 , Zhaoming Zhang 7 , Brendan J. Kennedy 1
Affiliation  

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 Pmm. 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 Pmm 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.

中文翻译:


通过 X 射线光谱和中子总散射研究 CaTi1–xFexO3–x/2 钙钛矿中新出现的阴离子无序



钙钛矿型 CaTi 1– x Fe x O 3– x /2 (0.00 ≤ x ≤ 0.40) 氧化物的长程平均和短程局部结构已使用高分辨率同步加速器 X 射线衍射 (SXRD) 确定)、中子粉末衍射(NPD)和中子对分布函数(NPDF)方法,并得到 X 射线吸收近边缘结构光谱(XANES)的支持。 Fe 3+部分取代 Ti 4+导致长程平均结构的对称性从斜方Pbnm增加到立方Pmm 。这也导致阴离子空位的引入,阴离子亚晶格无序,在 NPD 中观察到广泛的漫反射。掺杂后Fe L 3边缘特征的变化表明Fe 3+配位环境发生显着变化。然而,在Ti L 3边缘光谱中仅观察到细微的变化,这表明氧空位主要位于Fe 3+阳离子周围。 NPDF 分析证实阴离子空位优先位于 Fe 3+阳离子周围,导致形成一系列不同尺寸的 FeO n ( n = 4, 5, 6) 多面体和无序多面体倾斜。从长程斜方Pbnm到立方Pmm结构的变化与Ca 2+偏心和位移的变化密切相关。 我们将我们的发现与之前报道的这些组合物的离子电导率联系起来,以获得完整的结构-性能关系。这项工作揭示了超出平均结构的局部和可工程的结构复杂性,并提高了我们对钙钛矿在固态离子导体和氧传输膜中的结构-性能关系的理解。
更新日期:2024-09-11
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