封面文章
Atomic insights into topochemical fluorination and strong octahedral tilt in La2CoO4
Yuzhou He(何玉洲), Ting Lin(林挺), Shiyu Wang(王诗雨), Ang Gao(高昂), Ziang Meng(孟子昂), Tianping Ying(应天平), Zhiqi Liu(刘知琪), Lin Gu(谷林), Qinghua Zhang(张庆华), and Binghui Ge(葛炳辉)
Chin. Phys. B, 2025, 34 (7): 076102
文章亮点介绍
钙钛矿氧化物的阴离子调控工程是调控材料电子结构与物性的重要手段，传统研究多依赖如X射线衍射、中子衍射等平均化表征手段，难以解析局部畸变与动态位点竞争，导致阴离子取代路径及阴离子有序化规律长期存在争议。
本文选取层状Ruddlesden-Popper结构La2CoO4为模型体系，通过低温拓扑化学进行氟化，旨在揭示氟取代的动态路径及其对材料性能的调控机制。结合球差校正透射电子显微术（STEM）与电子能量损失谱（EELS），实现了氟/氧原子占据位点的直接成像与定量解析。研究表明，氟化过程中氟优先取代八面体顶端氧位点，诱导电子态演变与八面体倾转；首次发现了中间相La2CoO3.5F，并揭示了氟化从顶端取代到间隙位点填充的动态路径。本文的研究为层状氧化物的阴离子动态过程解析提供了新范式。
Fig. 1. Octahedral tilt of La2CoO4 and three oxyfluorides. (a)–(d) Annular bright field (ABF) images of the pristine La2CoO4, stage I (La2CoO3.5F), stage II (La2CoO3F2), and stage III (La2CoO2.5F3) along the [110] zone axis, respectively. Scale bar: 0.5 nm. The model in the lower left corner illustrates the octahedral distortion between neighboring layers. In stages I–III, the anions filling the interstitial sites are marked by yellow/red dashed circles, and simulated ABF images are shown in the lower right corner. (e)–(h) Corresponding Co–O1–Co bond angles and Co–O1 bond lengths of the octahedra in La2CoO4 and three oxyfluorides shown in (a)–(d).
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https://iopscience.iop.org/journal/1674-1056
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