Ion conductivity and diffusion in ZrF 4-based fluoride glasses containing LiF (0≤ xLiF≤0.60)

Abstract

Electrical and diffusion properties of two complementary series of ZrF 4-based fluoride glasses containing LiF were examined as a function of LiF content (0≤ x LiF≤0.60). The ac conductivity data have been analyzed by the complex modulus formalism and a hopping mechanism for transport is suggested. Experimental points representative of various electrical and diffusion parameters as a function of x LiF for the glasses studied are located on both sides of `master' curves. 19 F and 7 Li NMR investigations show that F − and Li + ions participate as charge carriers in the conduction mechanisms. The variation of electrical and diffusion properties with increasing x LiF have been explained by the crossing for x LiF≃0.20 from a conductivity due preferentially to F − ions to a conductivity due preferentially to Li + ions. A minimum of the decoupling index, R τ ( T g), is shown for x LiF≃0.20, in agreement with the conductivity minimum observed for the same x LiF content. Variation of the β conductivity relaxation parameter involves a minimum for x LiF≃0.35. A structural origin is proposed for such a minimum, the existence of which has been previously shown for x NaF≃0.40 in the homologous fluoride glasses containing NaF.