The Role of Titania in Silica Glasses

A series of glasses in the system Na 2 O–SiO 2 –TiO 2 were melted. Density measurements and refractive indices were determined. Molar refractions of the various glasses were calculated using the Lorentz‐Lorenz relationship. The partial molar refraction of TiO 2 , as determined in glass, corresponds closely with the values obtained from crystalline compounds and indicates that the Ti 4+ ion exists in sixfold coordination. Interionic distances were calculated using the Kordes equation, the calculated Si–O distance being 1.60 a.u. and the Ti–O distance, equal to 2.01 a.u.