NMR and impedance spectroscopy data on the ionic mobility and conductivity in PbSnF4 doped with alkali metal fluoride

Abstract

NMR and impedance spectroscopy are used to study the ionic mobility and conductivity in crystalline samples in PbSnF 4 -MF systems (M = Li, Na, K) in a 150-473 K temperature range. The 19 F NMR spectral parameters, types of ionic motion, and ionic conductivity value in the PbSnF 4 compound doped with alkali metal fluoride is found to be determined by the temperature, nature, and concentration of an alkali cation. The specific conductivity of the crystalline samples in PbSnF 4 -MF systems (M = Li, Na, K) is rather high at room temperature and hence, it seems possible to apply them in the development of functional materials with high ionic (superionic) conductivity.One of the aspects in the study of fluoride systems is the examination of the ionic mobility and transport. Ionic conductors with high conductivity through fluoride ions are promising materials for various electrochemical devices, chemical sensors, and so on. Fluoride ions being the lightest of anions (except a hydride ion) have a sufficiently high redox potential, which provides favorable conditions for the use of fluorides in batteries with high specific energy. Fluorides of heavy metals, such as LaF 3 , CeF 3 , PbF 2 , SnF 2 , BiF 3 and materials based on them, can be related to fluoride-containing compounds with high ionic conductivity [1]. This is explained by high polarizability of large-size cations (low ionization energy), which results in a decrease in the activation energy of ion transfer. Among numerous fluoride-containing compounds and solid solutions with high ionic conductivity, SnF 2 -based solid electrolytes are of great interest [2], and among them, compounds of the composition MSnF 4 , in particular, the PbSnF 4 compound, have the best electrophysical properties [2][3][4][5][6][7][8]. Note that the structure and properties of the PbSnF 4 compound (including phase transitions, ionic mobility, transport, and conductivity, etc.) were considered in a number of works [2][3][4][5][6][7][8][9][10][11][12], and some ambiguity in the results of these studies is due to complex polymorphism inherent in this compound [2,7,10].The nature of the outer-sphere cation is known to substantially affect the structure and properties of complex stannate(II) fluorides [2,10,13]. Variation of the cation sublattice composition often leads to the formation of compounds that differ in the structure and energy of ionic motion. It is of interest to answer the question: how does the character of dynamic processes change in the PbSnF 4 compound if part of cations is substituted with other cations? It is exemplified by the results of the analysis of ionic conductivity in tetragonal PbSnF 4 , in which part of Pb 2+ and/or Sn 2+ ions were replaced

Fluoride ion batteries – past, present, and future

“…66 19 F MAS NMR results show the that mechanochemical synthesis drives the system mainly into the cubic β-phase, with the introduction of surface defects, which exchange with the ix Copyright © 2018, American Chemical Society nanoparticle core. 66,67 This interaction also promotes conductivities within the crystallite and at the particle boundaries, with ion mobility at the macroscopic material level, which is in slight contrast to what is reported in previous studies. [68][69][70] Low activation energies result in high ionic conductivities at room temperature (Figure 10b), with values close to single crystals and better than what was found previously for fluorite type materials.…”

Fluoride ion conductivity of solid solutions KxPb0.86-xSn1.14F4-x

“…This anions redistribution in inherent in the overwhelming majority of fluoride ion conducting phases with fluorite and tysonite structures. 32 The transformation of the resonance band shape in the temperature range of 150-453 K entails a significant decrease in ∆Н from 96 to 5 kHz (Fig. 6).…”

“…The appearance of the obtained spectra indicates that the fluorine anions occupy structurally different positions in the lattice. 31,32 There are distinguished position F(1) in a rigid lattice with immobile anions, which are on triple axes, position F(2) with locally mobile anions on the same axes and interstitial fluorine anions F(3). With increasing the temperature, a redistribution of fluorine anions between the positions occupied by them in the lattice takes place.…”

“…With increasing the temperature, a redistribution of fluorine anions between the positions occupied by them in the lattice takes place. 31,32 The narrow spectral component characterizing highly mobile interstitial ions becomes predominant in integrated intensity. This anions redistribution in inherent in the overwhelming majority of fluoride ion conducting phases with fluorite and tysonite structures.…”

CONDUCTIVITY OF SOLID FLUORIDE-CONDUC­TING PHASES BaxPb0.86-xSn1.14F4

“…Розрізняють позицію F(1) жорсткої ґратки з нерухомими аніонами, що знаходяться на осях третього порядку, позицію F(2) з локально рухливими аніонами на тих самих осях та міжвузлові аніони фтору F(3). Зі збільшенням температури відбувається перерозподіл аніонів фтору між позиціями, які вони займають у кристалічній ґратці [13][14]. Домінуючою за інтегральною інтенсивністю стає вузька складова спектра, що характеризує високорухливі міжвузлові йони.…”