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Synthesis and X-ray-graphical characteristics of the MеSn2F5 (Mе = Na, K, Rb, Cs) fluoride-ion conductors

https://doi.org/10.32362/2410-6593-2021-16-5-426-437

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Abstract

Objectives. Pentafluorodistannates of alkali metals are promising materials for use as electrolytes in fluoride-ion batteries due to their electrophysical properties, such as high fluoride-ion conductivity. This work aims to synthesize crystals of alkali metals MeSn2F5 (Me = Na, K, Rb, Cs), carry out X-ray diffraction studies on them, and investigate the possibility of obtaining lithium fluorostannates.

Methods. Supersaturated aqueous solutions were employed to synthesize the crystals. The X-ray diffraction (XRD) analysis was carried out.

Results. Oversaturated solutions yield microcrystalline powders of sodium, potassium, rubidium, and cesium pentafluorodistannates. The presence of a single-phase was confirmed by XRD analysis of the powders corresponding to the MеSn2F5 (Mе = Na, K, Rb, Cs) composition. XRD data analysis and literature indicated that MеSn2F5 (Mе = K, Rb, Cs) have a fluorite-like structure, with the cations forming three-layer closest packing. The RbSn2F5 compound was discovered to be isostructural to KSn2F5. Based on this discovery, RbSn2F5 was reindexed to a hexagonal unit cell with parameters a = 7.40(3) Å, с = 10.12(6) Å (KSn2F5 P3, a = 7.29(3) Å, с = 9.86(2) Å). The CsSn2F5 compound was reindexed to a monoclinic unit cell (a = 10.03(4) Å, b = 5.92(7) Å, c = 11.96(9) Å, β = 107.4(5)°). A crystallochemical analysis of the pentafluorodistannates was carried out, and common structural motifs were discovered. The motifs are similar to lead tetrafluorostannate PbSnF4, the best fluoride-ion conductor. The effect of the pentafluorodistannates structures on the ionic conductivity is considered. The LiF–SnF2 system contains no compounds; the compositions were obtained by melting the original fluorides.

Conclusions. MеSn2F5 (Mе = Na, K, Rb, Cs) were synthesized and investigated by XRD analysis. The structural characteristics of the RbSn2F5 and CsSn2F5 compounds have been redefined. The crystallochemical structure is analyzed in relation to the electrophysical properties of the alkali metal pentafluorodistannates. Pentafluorodistannates MеSn2F5 (Mе = K, Rb, Cs) have a fluorite-like structural motif with cubic parameters а = 5.694 Å (KSn2F5), а = 5.846 Å (RbSn2F5), а = 6.100 Å (CsSn2F5), with the cations forming three-layer closest packing. The cationic layers alternate like Me–Sn–Sn–Me (Mе = K, Rb, Cs). For KSn2F5 and RbSn2F5, they are normal to the three-fold axis and normal to the four-fold axis in the case of CsSn2F5.

About the Authors

R. M. Zakalyukin
MIREA – Russian Technological University; Federal Scientific Research Center “Crystallography and Photonics,” Russian Academy of Sciences
Russian Federation

 Cand. Sci. (Chem.), Senior Lecturer, Department of Electrotechnical Systems, Institute of Radio Engineering and Telecommunication Systems; Senior Researcher

86, Vernadskogo pr., Moscow, 119571, Russia

59, Leninskii pr., Moscow, 119333, Russia

Scopus Author ID 6602502445, ResearcherID O-3799-2014



E. A. Levkevich
MIREA – Russian Technological University; Federal Scientific Research Center “Crystallography and Photonics,” Russian Academy of Sciences
Russian Federation

 Teaching Assistant, Department of Electrotechnical Systems, Institute of Radio Engineering and Telecommunication Systems;
Postgraduate Student

86, Vernadskogo pr., Moscow, 119571, Russia

59, Leninskii pr., Moscow, 119333, Russia

Scopus Author ID 57207661566, ResearcherID Z-1981-2018



A. V. Nikolaeva
Lomonosov Moscow State University
Russian Federation

 Student, Faculty of Chemistry

1, Leninskie gory, Moscow, 119991, Russia



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  • Cations of MeSn2F5 (Me = K, Rb, Cs) pentafluorodistannates form a three-layer closest packing (fluorite-like cell with parameter a) with alternating layers in Me–Sn–Sn–Me sequence (Me = K, Rb, Cs) perpendicular to the three-fold axis in the case of KSn2F5 and RbSn2F5, and four-fold axis in the case of CsSn2F5.
  • Potassium and rubidium pentafluorodistannates are isostructural and are represented by the space group P
  • Cesium pentafluorodistannate has a different packing of cations; the compound is reindexed in a monoclinic cell.

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For citations:


Zakalyukin R.M., Levkevich E.A., Nikolaeva A.V. Synthesis and X-ray-graphical characteristics of the MеSn2F5 (Mе = Na, K, Rb, Cs) fluoride-ion conductors. Fine Chemical Technologies. 2021;16(5):426-437. https://doi.org/10.32362/2410-6593-2021-16-5-426-437

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