The general refractivity formula applied to densified silicate glasses

Concomitant changes of refractive index (n) with density (ϱ) of isochemical series comprizing several densified silicate glasses were analyzed. The data include glasses of the systems SiO₂, TiO₂-SiO₂, Na₂O-SiO₂, and NaAlSi₃O₈-CaAl₂Si₂O₈. Extending the ideal point dipole theory, an electronic overlap parameter (b) accounting for the non-ideal behaviour of solids was refined using the general refractivity formula , where α is the molar polarizability. Statistical analyses assuming α=constant within each isochemical series showed no systematic variation of b with chemical composition. A constrained refinement of b using all data converged at b=1.3. Applying this common overlap parameter and appropriate polarizability constants, recalculated refractive index values fit excellently the experimental results within the entire n−ϱ range. Furthermore, the additivity of polarizabilities, often assumed for oxide components, is derived for TiO₂-SiO₂ glasses and for glasses of plagioclase composition.