Systematics of defect structures in glasses with ionic substitutions

Abstract

The effects of various ionic substitutions on defect structures in glass were investigated in soda-lime-silica systems. It is shown that detailed measurements of flaw characteristics provide a useful tool for investigating subtle internal energy variations in this solid. Influences of specific ions were quantitatively studied by determining the parameters of flaw length (F1), and flaw number (Fn). Flaws produced on freshly broken surfaces under controlled loading conditions, were shown to be a direct indication of the stress response of the glass network. Relative bond strength and rigidity or brittleness of the structures varied with the ionic field strengths of added cations. Alkali ions in the form of oxides, were substituted for sodium and alkaline earth ions for calcium. Other additions and substitutional ions were also studied in detail. In general, the changes in flaw parameters were found to agree with theoretical predictions of internal energy changes based on the manner in which the ion entered the network, that is, as a lattice modifier, interstitial or network former. In specific systems, the variations in flaw length and flaw numbers were tentatively explained by changes in defect concentration and free volume as the ions were substituted.