Refractive index-structure correlations in Na2O–Al2O3–SiO2 glasses

Abstract The current structural models have been used to analyse the refractive index data of Na 2 O–Al 2 O 3 –SiO 2 glasses (Al 2 O 3 /Na 2 O⩽1). The SiO 2 content is the sole factor that controls the refractive index. Values could be obtained for the factors with which each structural unit contributes in the refractive index. The content of Al 2 O 3 or Na 2 O has no effect on the refractive index. The factors (differential refraction) are constant and do not change with composition. They have the same values for Na 2 O–SiO 2 glasses. The differential refraction of a structural unit increases linearly with increasing the number of non-bridging oxygen ions. The difference of the contribution to the refractive index from a silicate unit to the next equals to a half of that for AlO 4 tetrahedron. The effect could be attributed to the change in both the concentration and differential refraction of structural units. The obtained factors for the structural units are useful in calculating the refractive index with a high degree of accuracy.