Considerations on the structure and physical properties of B2O3–SiO2 and GeO2–SiO2 glasses

Data of density, refractive index and thermal expansion coefficient for B2O3–SiO2 and GeO2–SiO2 glasses have been analyzed. The volumes of the structural units are the same found for the vitreous B2O3, GeO2 and SiO2. The volume of any structural unit is constant over the entire composition region of the glass system. The same has been found for the differential refraction and unit refraction of the structural units in these glasses. Different features are observed for the differential expansion of the structural units. There is a considerable change with composition in the differential expansion of BO3, GeO4 and SiO4 units. The effect is attributed to a change in the asymmetry of vibrations with the number of Si–O–B or Si–O–Ge linkages in the matrix. The thermal expansion coefficient is mainly determined by the contribution of B2O3 or GeO2 in the concerned glasses.