Structural correlations in the ac conductivity of ion-containing glasses

The power law dispersion of the conductivity in most ion-containing oxide glasses appears to be universal. This universality indicates that no correspondence exists between the degree of non-Debye behavior and the microscopic structure of a glass host. Despite its universal frequency dependence, we demonstrate how the ac conductivity defines a special length scale, L, that represents average diffusional displacement of an ion per activated jump and which can be correlated to properties of the glass host. We compare this length scale to the inter-ionic spacing and demonstrate how both increase with decreasing ion concentration. Although there is much evidence for universality, we suggest that the conductivity exponent may in fact be influenced by the 'dimensionality' of the conduction process.