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-ray 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 maintaining the SiO4 tetrahedra. Silver was introduced by substituting for sodium, according to the glass composition. A relaxation of the glass structure was performed using pair and multibody potential functions. By comparison of the experimentally obtained correlation functions with the calculated ones, the assumption was confirmed that the ion exchange causes structural rearrangements within the short range order, as well as attractive Ag-Ag interactions, well below the glass transformation temperature.