High temperature Raman spectra of sodium disilicate crystal, glass and itsliquid

Raman spectra of Na2Si2O5 in solid and liquid states from room temperature to 1773 K were measured to observe phase transition and analyze the tempera ture-dependent variations of the structure units, five kinds of SiO4 tetrah edrons, which are defined as Q(4), Q(3), Q(2), Q(1) and Q(0) species corres ponding to the number of bridging oxygen binding to each Si. A pulsed coppe r vapor laser was used as laser source coupled with time resolved detection system to eliminate the dense thermal emission background while temperatur e was >1273 K. Temperature-dependent Raman spectra can clearly indicate mel ting point of a crystal around 1143 K. Gaussian deconvolutions of complex s tretching vibrational bands of crystal and amorphous states (glass and liqu id) were described. Raman sensitivity factors were introduced to calculate the mole fractions of the different SiO4 tetrahedrons. There is a decrease of Q(3) species and an increase of Q(4) and Q(2) species with increasing te mperature. 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 gla ss is similar to that of the liquid of melting temperature, T-m similar to 1143 K, the liquid structure has a greater disorder than that of the glass. (C) 2001 Published by Elsevier Science B.V.