, Volume 15, Issue 4, pp 363-369

The general refractivity formula applied to densified silicate glasses

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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 \(\frac{{n^2 - 1}}{{4\pi + b\left( {n^2 - 1} \right)}}\frac{1}{\rho } = \alpha /M\) , 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.