<br>Cubic-BaSnF4 中的动态孤对电子和氟离子无序,Journal of the American Chemical Society

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Cubic-BaSnF4 中的动态孤对电子和氟离子无序
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-10-16 , DOI: 10.1021/jacs.3c08232
Briséïs Mercadier _{1,

2,

3} , Samuel W Coles _{4,

5} , Mathieu Duttine ₆ , Christophe Legein ₇ , Monique Body ₇ , Olaf J Borkiewicz ₈ , Oleg Lebedev ₉ , Benjamin J Morgan _{4,

5} , Christian Masquelier _{1,

3} , Damien Dambournet _{1,

2}

Affiliation

在结晶固体电解质中引入成分或结构无序是提高其离子电导率的常见策略。（男，Sn）F₂ 萤石先前被认为在其阳离子宿主框架内表现出两种形式的无序：来自随机分布的 M 和 Sn 阳离子的职业障碍和来自 Sn（II）立体活性孤对电子的定向障碍。在这里，我们结合使用实验和计算技术来表征立方 BaSnF₄ 的结构和氟离子动力学。X 射线衍射（XRD）数据的 Rietveld 精修证实了具有 {Ba，Sn} 阳离子无序的平均萤石结构，^{而 119}Sn Mössbauer 光谱证明了立体活性 Sn（II）孤对电子的存在。X 射线全散射 PDF 分析和从头到尾的分子动力学模拟揭示了一个复杂的局部结构，具有高度的固有氟离子无序，其中 1/3 的氟离子占据八面体“间隙”位点：这种氟离子无序是 Sn 孤对电子和氟离子之间排斥的结果，使 Sn 配位四面体氟离子位点不稳定。变温 ¹⁹F NMR 实验和分子动力学模拟分析揭示了高度不均匀的氟离子动力学，富 Sn 局部环境中的氟离子比富 Ba环境中的氟离子移动性强。我们的模拟还揭示了 Sn 孤对电子的动力学重新取向，该取向受局部阳离子构型偏倚并与局部氟离子动力学耦合。最后，我们讨论了宿主框架无序对立方 BaSnF 中长程扩散途径的影响₄。

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Dynamic Lone Pairs and Fluoride-Ion Disorder in Cubic-BaSnF4

Introducing compositional or structural disorder within crystalline solid electrolytes is a common strategy for increasing their ionic conductivity. (M,Sn)F₂ fluorites have previously been proposed to exhibit two forms of disorder within their cationic host frameworks: occupational disorder from randomly distributed M and Sn cations and orientational disorder from Sn(II) stereoactive lone pairs. Here, we characterize the structure and fluoride-ion dynamics of cubic BaSnF₄, using a combination of experimental and computational techniques. Rietveld refinement of the X-ray diffraction (XRD) data confirms an average fluorite structure with {Ba,Sn} cation disorder, and the ¹¹⁹Sn Mössbauer spectrum demonstrates the presence of stereoactive Sn(II) lone pairs. X-ray total-scattering PDF analysis and ab initio molecular dynamics simulations reveal a complex local structure with a high degree of intrinsic fluoride-ion disorder, where 1/3 of fluoride ions occupy octahedral “interstitial” sites: this fluoride-ion disorder is a consequence of repulsion between Sn lone pairs and fluoride ions that destabilizes Sn-coordinated tetrahedral fluoride-ion sites. Variable-temperature ¹⁹F NMR experiments and analysis of our molecular dynamics simulations reveal highly inhomogeneous fluoride-ion dynamics, with fluoride ions in Sn-rich local environments significantly more mobile than those in Ba-rich environments. Our simulations also reveal dynamical reorientation of the Sn lone pairs that is biased by the local cation configuration and coupled to the local fluoride-ion dynamics. We end by discussing the effect of host-framework disorder on long-range diffusion pathways in cubic BaSnF₄.

更新日期：2023-10-16

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