Abstract
The weak-electrolyte theory relates the considerable variations in the ionic conduction of glasses as a function of composition to variations in the thermodynamic activity of network modifiers. In this work, a simple thermodynamic model has been developed based on the existence of three possible configurations for oxygen or sulphur. It has been used to calculate the variations in modifier activity and thus to justify the variations in ionic conduction and activation energy with composition. The validity of the model has been tested using results for Li+-conducting oxide and sulphide binary glasses.