In-situ high temperature Raman and Brillouin light scattering studies of sodium silicate glasses

In-situ Raman and Brillouin light scattering experiments were carried out to study the structure and elastic properties of sodium silicate glasses xNa2O–(100 − x)SiO2 (x = 0, 8, 10, 15, 20, 25, 30, and 40 mol%) from room temperature up to the respective glass transition temperature for each composition. Temperature independent shear modulus and Youngʹs modulus were observed in 15Na2O–85SiO2 glass up to 400 °C, while the temperature independent bulk modulus occurred in glass with 15 to 20 mol% Na2O in the same temperature range. A simple correlation was established between the Raman spectrum of a sodium silicate glass at room temperature and the evolution of its elastic properties with increasing temperature. The silica network stiffens upon heating up due to the conformation change from α-like to β-like rings in silica-rich sodium silicate glasses, characterized by the main band at ~ 440 cm− 1 in Raman spectra. When the 950 cm− 1 band associated with the Q2 species becomes obvious after substantial amount of Na2O was added into the glass matrix, glasses behave like normal solids (softening upon heating up). If neither the main band at ~ 440 cm− 1 nor the 950 cm− 1 band is well defined, intermediate glasses emerge, whose elastic moduli do not change with temperature because the stiffening and softening effects become comparable.