COMPUTER-GENERATED RANDOM NETWORK MODELS OF ION-EXCHANGED GLASSES

Structural models of sodium silicate glasses with reference to silver- sodium ion exchange have been created on the basis of an extended X-ra y absorption fine structure study. A random network model derived from the crystal structure of alpha-Na2Si2O5 was generated by successively converting sixfold rings into fivefold and sevenfold rings, while mai ntaining the SiO4 tetrahedra. Silver was introduced by substituting fo r sodium, according to the glass composition. A relaxation of the glas s structure was performed using pair and multibody potential functions . By comparison of the experimentally obtained correlation functions w ith the calculated ones, the assumption was confirmed that the ion exc hange causes structural rearrangements within the short range order, a s well as attractive Ag-Ag interactions, well below the glass transfor mation temperature.