CATION ENVIRONMENTS AND THE MIXED ALKALI EFFECT IN SILICATE-GLASSES - AN EXAFS INVESTIGATION

EXAFS measurements have been used to obtain the environments of salient cations in a variety of binary alkali silicate glasses. Compared to SiO2 a lengthening of the mean tetrahedral Si-O bond length is observed. K-O and Cs-O bond lengths and coordination numbers indicate these alkalis and their nearest neighbour oxygens occupy quasi-octahedral sites in single alkali glasses. Small differences are observed when both alkalis are present, indicating intimate mixing. This is predicted by the Modified Random Network (MRN) which is used to provide a unified picture for the Mixed Alkali Effect based on structural constraint.