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

Briséïs Mercadier, Samuel W. Coles, Mathieu Duttine, Christophe Legein, Monique Body, Olaf J. Borkiewicz, Oleg Lebedev, Benjamin J. Morgan, Christian Masquelier, Damien Dambournet

Research output: Contribution to journalArticlepeer-review

1 Citation (SciVal)

Abstract

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.

Original languageEnglish
Pages (from-to)23739-23754
Number of pages16
JournalJournal of the American Chemical Society
Volume145
Issue number43
Early online date16 Oct 2023
DOIs
Publication statusPublished - 1 Nov 2023

Bibliographical note

Funder(s) & Grant ID(s)
Royal Society - URF\R\191006; Argonne National Laboratory - DE-AC02-06CH11357; Agence Nationale de la Recherche - ANR-10-LABX-76-01; Faraday Institution - FIRG016; Research Councils UK - EP/S003053/1

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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