Activation volume and free volume in some ion-conducting glasses and molten salts

In an ion-conducting glass or molten salt the ions conduct via the voids. The void volume is characterized in terms of the free volume. On the other hand, when the material is pressurized, its ionic conductivity decreases. This reduction is expressed using a parameter denoted as the activation volume. The present author proposed recently that the free volume is made of the structural part, due to the disordered structure, and the atomic part which is inherent in the constituent atoms themselves. Comparison is made between the free volume and the activation volume.