Information on the absolute length scales of ion transport processes in glasses from electrical conductivity and tracer diffusion data

We show that absolute values for the time-dependent mean-square displacement of mobile ions in glasses can be obtained from a combined analysis of electrical conductivity and tracer diffusion data. By applying this method to sodium germanate glasses of different compositions, we find that the distances the ions cover in characteristic stages of the transport process increase considerably with decreasing sodium oxide content. At low sodium oxide contents, we observe a linear relation between the transport distances and the interionic separation distances, while this relation is lost at high sodium oxide contents. The same is found to be true for other alkali ion conducting glassy systems. The analysis of this effect is important for discriminating between the influence of the network structure and of the interionic Coulomb interactions on the ion dynamics. (C) 1999 Elsevier Science B.V. All rights reserved.