Correlation between Free Volume and Ionic Conductivity in Fast Ion Conducting Glasses.

Abstract

It is well known that fast ionic conductivity can be obtained by doping modified oxide glasses with a metal-halide salt. The role of the dopant salt, apart from providing additional charge carriers, for the ionic conductivity has been a much debated issue. Using conductivity and density data for different host glasses mixed with various metal-halide salts, we find a remarkable common cubic scaling relation between the conductivity enhancement and the expansion of the network forming units induced by salt doping. This suggests that the glass network expansion, which is related to the available free volume, is a key parameter determining the increase of the high ionic conductivity in this type of fast ion conducting glasses. [S0031-9007(96)01369-5] High room temperature ionic conductivity in solid materials is technologically interesting for various solid state electrochemical devices, e.g., batteries, “smart windows”. Apart from some exotic crystalline materials such as Rb4AgI5, the highest ionic conductivity at room temperature has been observed in some salt doped oxide, sulfur, and halide glasses. The salt doped oxide glasses are particularly interesting for applications because of their ease of preparation, their stability, and the large available composition ranges, and have also become model materials for investigations of diffusion in disordered solids.