Ion conductivity and diffusion in ZrF4-based fluoride glasses containing LiF (0<=x(LiF)<=0.60)

Electrical and diffusion properties of two complementary series of ZrF4-based fluoride glasses containing LiF were examined as a function of LiF content (0 less than or equal to x(LiF) less than or equal to 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. F-19 and Li-7 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) similar or equal to 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(tau)(T-g), is shown for x(LiF) similar or equal to 0.20, in agreement with the conductivity minimum observed for the same x(LiF) content. Variation of the beta conductivity relaxation parameter involves a minimun for x(LiF) similar or equal to 0.35. A structural origin is proposed for such a minimum, the existence of which has been previously shown for x(NaF) similar or equal to 0.40 in the homologous fluoride glasses containing NaF.