Fluoride-ion conductors

Aliovalent doping can also be used to enhance low temperature conductivities. Both interstitial F ions and F vacancies can be generated in, for example, CaF2 by doping with Na and La, respectively (Kudo and Fueki, 1990). 

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FIGURE 25.7 Conductivity of some fluoride ion conductors as a function of 1/7. (From Gelings and Bouwmeester, 1997, Fig. 6.3, with permission from CRC Press LLC via CCC.)... 

Figure 6.24 Ionic conductivity of fluoride-ion conductors. For comparison, data for typical Li, Na", Ag" and ion conductors are also shown. (After Hagenmuller, 1983

Much of the structural data are based on powder X-ray diffraction, but structures are typically polymeric with the bismuth in a distorted nine-coordinate environment similar to that in BiF3 or the Tysonite structure. There has been considerable interest in these compounds as fast fluoride ion conductors. ... 

Reau, J. M. Grannec, J. In Inorganic Solid Fluorides, Hagenmuller, P. Ed. Academic Press New York, 1985 Chapter 12, Fast fluoride ion conductors, pp 423-461. 

F, 87Rb and 119Sn NMR spectra were used to characterise the two-dimensional fluoride-ion conductor RbSn2F5 26 Proton NMR studies helped to construct the P-T phase diagram (95-300 K, 0-800, MPa) for Rb x(NH4)xI, where x = 0.29 or 0.77.27... 

Several fluorides form the cubic fluorite structure (including CaF2 for which it is named), and are excellent fluoride ion conductors [50] (see Chapter 2). With the introduction of an oxide phase, either during fabrication or in situ during operation, fluoride ion conductors can be used as electrolytes in oxygen sensors [51]. One ofthe advantages of using fluoride electrolytes is that they tend to remain pure ionic... 

Rare-earth elements are vital constituents of several prominent high-temperature solid electrolytes ranging from oxygen- or fluoride-ion conductors in the fluorite structures to protonic conductors in the doped perovskite phases and trivalent-ion conduction in Sc2(W04)3 and 3-alumina-type compounds. Solid electrolytes are considered as important for scientific studies and technological applications in vital areas such as fuel cells, batteries, sensors, process control and environmental protection. 

Oxygen and Other Sensors Based on Fluoride Ion Conductors. 214... 

When the lone pair is stereoactive, the compounds are insulators unless another conduction mechanism is present. This happens mostly in the tin(ll)-containing fluorides that have the fluorite-type structure or a structure derived from it, such as in SnFi and the MSnp4 compounds. In the latter, the presence of covalently bonded tin(ll) in a structure that is typically ionic creates a sufficiently large number of disorder on the fluoride sublattice to make the compounds the most efficient fluoride ion conductors [71,72]. 

At present, various oxygen sensors using metal oxide ionic conductors or oxide saniconductors are available for a wide variety of applications. It was shown that fluoride ion conductors such as LaFj, PbFj (Yamazoe and Miura 1990), and PbSnF (Kuwato et al. 1990,1997 Wakagi and Kuwano 1994) can also be used for these purposes. Table 6.5 summarizes solid-state oxygen sensors based on fluoride... 

Table 6.5 Oxygen sensors based on fluoride ion conductors...

G. Denes, Y.H. Yu, T. Tyliszczac, A.P. Hitchcock, Sn-K and Pb-Ls EXAFS, X-Ray Diffraction, and Sn Mossbauer Spectroscopic Studies of Ordered /3-PbSnF4 and Disordered Pbi, Snj2 (x = 0.3, 0.4) Solid Solutions and PhSotFio High Performance Fluoride Ion Conductors, J. Solid State Chem., 104, 239-252 (1993). 

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