Concentration fluctuations and electrical properties of some ionic conductive silica-based glasses

Abstract

An original method is proposed for the investigation of concentration fluctuations in ionic conductive glasses. The electrical impedances of M 2OSiO 2 ( M  Li, Na, K, Rb) M + ion conducting glasses have been measured in the 5 Hz-500 kHz frequency range. Complex impedance plots exhibit arcs of circle characteristic of R-C type conduction relaxation. The experimental curves have been interpreted by assuming the existence of a dispersion on R (or on the conductivity σ) in the bulk. With this hypothesis, an analytical formalism is proposed which allows the mean square fluctuations in conductivity to be calculated for the investigated glass samples. Taking into account the conductivity-alkali oxide dependence, mean square fluctuations in concentration can be estimated 〈( ΔC) 2〉. Two ways are followed for verifying the so-obtained values: 1. (i) thermodynamic fluctuation theory of liquids has been applied for vitreous materials assuming that a glass retains the configurational fluctuations of the liquid at the glass transition temperature T g. V〈( δC) 2〉 values have been calculated by this way with the help of emf measurements performed on different concentration cells or by using a previously established relation (σ = ka m 2O 1 2 2. (ii) Small angle neutron scattering (SANS) intensity measurements have been realized which exhibits a Q range ( Q is the magnitude of the scattering vector) characteristic of thermal density and concentration fluctuations. V〈 δC 2〈 values have been calculated from absolute scattering cross-section magnitudes. V values deduced from the comparison between the proposed methods suggest an ion jump distance of about 6 Å in silica-based glasses.