FLUORIDE-ION CONDUCTION AND ITS MECHANISM IN FLUORIDE GLASSES

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1. Electrical conductivity measurements by ac methods were made of Al <F_3> -, Hf <F_4> -, Sc <F_3> -, Zn <F_2> -, Zr <F_4> -, Ga <F_3> -, Fe <F_3> - and In <F_3> -based fluoride glasses. The conductivities of the examined glasses ranged from about <10^(-6)> to about 10- <^2S> ・ <cm^(-1)> at 200゜C. The magnitude of conductivity, though it varies to some extent with glass composition, increased in the order described above. As the result a fluoride glass with a conductivity superior to that <beta> -Pb <F_2> was found in the In <F_3> -based glass system.2. The transport numbers of <F^-> ions were examined of Zr <F_4> -Ba <F_2> -CsF and Fe <F_3> -Mn <F_2> -Pb <F_2> glasses with relatively high electrical conductivities by the Tubandt and emf methods, respectively. The result revealed that the former glasses are purely <F^-> -ion conductors, while the latter glasses are mixed <F^-> -ion and electron conductors.3. Electrical conductivity and <^(19)F> -CW・NMR measurements were made of a BaZr … More <F_6> glass and <alpha> - and <beta> -BaZr <F_6> crystals. The NMR result elucidated that, in the glass and the crystals, there are two kinds of <F^-> -ion sites with different behaviors of motion. The electrical conductivity and NMR results clarified that the easiness of <F^-> -ion movement are in the order BaZr <F_6> glass, <beta> -BaZr <F_6> , <alpha> -BaZr <F_6> , indicating that a glassy state is favorable for <F^-> -ion conduction, compared with a crystalline state.4. Based on the compositional dependence of electrical conductivity of various fluoride glasses and Zr <F_4> -Ba <F_2> -CsF glasses, the followings were deduced on the <F^-> -ion conduction-determining factors: The conductivity of <F^-> ions in fluoride glasses are predominantly determined by the activation energies for conduction. The activation energy for conduction decreases with an increase in the average polarizability of glass-constituting cations and with a decrease in the single bond strengths between glass-forming cations and <F^-> ions. Less