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

Raman spectra of Na2Si2O5 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 SiO4 tetrahedrons, which are defined as Q4, Q3, Q2, Q1 and Q0 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 SiO4 tetrahedrons. There is a decrease of Q3 species and an increase of Q4 and Q2 species with increasing temperature. And after melting, the ratio of the components remain unchanged. Q3 species decomposes again after about 1573 K. More Qn species would form with increasing temperature. Although the Qn distribution of the glass is similar to that of the liquid of melting temperature, Tm∼1143 K, the liquid structure has a greater disorder than that of the glass.