Structure and properties in (Sr, Na) silicate glasses and melts

Configurational entropy is linked with the structure of Na(2)O-SrO-SiO(2) melts by combined viscometry and Raman spectroscopic investigations. From the viscosity measurements at low and high temperatures, we obtained the configurational entropy, S(conf) (using log eta=Ae+Be/TS(conf) where eta is the viscosity, T the temperature and Ae, Be two constants). From Raman spectroscopy, we obtained structural information about Q speciation. A rapid decrease in viscosity at low temperature is observed in the Sr-silicate melts on addition of Na(2)O. At high temperature, the viscosity is almost the same for the Sr-silicate and for Na-silicate melts. The configurational entropy for Sr/Na silicate glasses shows a small increase with SrO content and corresponds to a non-ideal variation, and is interpreted in terms of a non-random distribution of Na and Sr in the silicate network. The addition of Na(2)O to the Sr-silicate melts produces an increase of the intensity and frequency of the boson peak, the concentration of the Q(2) species and the fragility of the melt.