High temperature Raman spectra of sodium disilicate crystal, glass and its liquid

Abstract

Raman spectra of Na 2Si 2O 5 in solid and liquid states from room temperature to 1773 K were measured to observe phase transition and analyze the temperature-dependent variations of the structure units, five kinds of SiO 4 tetrahedrons, which are defined as Q 4, Q 3, Q 2, Q 1 and Q 0 species corresponding to the number of bridging oxygen binding to each Si. A pulsed copper vapor laser was used as laser source coupled with time resolved detection system to eliminate the dense thermal emission background while temperature was >1273 K. Temperature-dependent Raman spectra can clearly indicate melting point of a crystal around 1143 K. Gaussian deconvolutions of complex stretching vibrational bands of crystal and amorphous states (glass and liquid) were described. Raman sensitivity factors were introduced to calculate the mole fractions of the different SiO 4 tetrahedrons. There is a decrease of Q 3 species and an increase of Q 4 and Q 2 species with increasing temperature. And after melting, the ratio of the components remain unchanged. Q 3 species decomposes again after about 1573 K. More Q n species would form with increasing temperature. Although the Q n distribution of the glass is similar to that of the liquid of melting temperature, T m ∼1143 K, the liquid structure has a greater disorder than that of the glass.