It was recalled that the ionic conductivity of glass ceramics depended not only upon the partial conductivities of the different phases, and their volume fractions, but also upon the structure of the composite material. The conductivity could be drastically increased by enhancing the ionic mobility along grain boundaries. The conductivity of such materials was considered in terms of upper and lower bounds; depending upon the degree of information about the structure. An effective medium approach was used to describe the direct-current conductivity for some characteristic types of structure. This approach was extended to the frequency dependence of conductivity. The model was applied to experimental data on glass ceramics in the system. Various structures in this system were obtained; leading to an increase or decrease in conductivity by up to 3 orders of magnitude, as compared with compared the starting glass.

A.Runge, H.Kahnt: Berichte der Bunsengesellschaft für Physikalische Chemie, 1996, 100[9], 1526-30