Density-structure correlations in silicate glasses

A quantitative analysis has been carried out for the density data of CaO-SiO2, SrO-SiO2, BaO-SiO2 and CdO-SiO2 glasses. The analysis is based on a model that has been applied for alkali silicate glasses. The model makes it possible to calculate the volumes of the structural units and to plot the density-composition dependence for these glasses. The results show that CaO, SrO, BaO and CdO enter the structure as modifiers. The volume of a structural unit changes with the type, but not with the concentration, of the modifier. The volume increases linearly with the increase in the reciprocal of the field strength of the modifier ion. A linear dependence could be observed for alkali and alkaline earth silicate glasses. A general relation has been obtained to calculate the volume of the structural unit as a function of the radius and charge of the modifier ion and the number of non-bridging oxygen ions (NBOs). (C) 1999 Published by Elsevier Science B.V. All rights reserved.