Ion dynamics and mixed mobile ion effect in fluoride glasses

Abstract

We report the ionic relaxation and mixed mobile ion effect in 50ZrF₄-10BaF₂-10YF₃-(30-x)LiF-xNaF fluoride glass series, where fluorine anions participate in the diffusion process in addition to alkali cations, unlike mixed alkali oxide glasses and crystals. By analyzing the ion dynamics in the framework of a power-law model as well as modulus formalism we have observed mixed mobile ion effect in the dc conductivity and its activation energy, the crossover frequency and its activation energy, the conductivity relaxation frequency and its activation energy, and also in the decoupling index. We have correlated these phenomena with the fractal dimension of the conduction pathways in the mixed alkali fluoride glasses compared to the single alkali glasses. We have shown that the relaxation dynamics in mixed alkali fluoride glasses is independent of temperature but dependent on glass composition.