A unified site relaxation model for ion mobility in glassy materials

The unified site relaxation model combines key features of the earlier dynamic structure and jump relaxation models, and provides a coherent model of ionic transport processes in glassy materials. The essential idea is that mobile ions hop backwards and forwards many times before: (i) the Coulomb field is relaxed and (ii) the 'target site' adjusts itself to the needs of its new occupant. The other mobile ions and the network of the glass are both involved in this (unified) relaxation process. Manifestations of site relaxation are seen in the frequency dependence of the conductivity, in mechanical loss spectra and in many d.c. 'anomalies' such as the mixed cation effect.