Ion transport in glass: Influence of glassy structure on spatial extent of nonrandom ion hopping

On short time scales, the diffusion of mobile ions in glasses is nonrandom, i.e., the ions perform correlated forward-backward motions. By using linear response theory, we show in detail how typical distances characterizing the spatial extent of the nonrandom ionic diffusion can be derived from frequency-dependent conductivity data when the Haven ratio is known. We compare the dependence of these typical distances on the alkali content in germanate, borate, and silicate glasses. In all glasses, the typical distances decrease with increasing alkali oxide content. In the germanate and silicate glasses, the decrease is, however, more pronounced than in the borates. This network former effect points to the influence of the network structure on the spatial extent of the nonrandom diffusion.