Equilibrium Compressibilities and Density Fluctuations in K2O–SiO2 Glasses

The density fluctuations contributing to light scattering in a glass are governed by the flctive temperature of the glass and the equilibrium compressibility of the melt. Using ultrasonic velocity data for K₂O–SiO₂ melts, these compressibilities were evaluated, and the magnitude of the density fluctuations were calculated. In this system, the mean–square amplitude of the fluctuations reaches a minimum value (about half that of pure SiO₂) for a composition of ∼20 mol% K₂O. By extrapolating the equilibrium compressibilities to zero K₂O content, the density fluctuations can be calculated for pure SiO₂ glass; this calculation agrees well with the result obtained from light–scattering measurements.