Microinhomogeneities of glasses of the system PbO-SiO2

Small angle x-ray scattering (SAXS) and Rayleigh-Mandelstam-Brillouin (RMB) light scattering as well as ultrasonic sound velocities have been studied in glasses of the system PbO-SiO2 which has an unusually wide range of glass forming ability. The results of scattering are compared with calculations based on the concept of frozen-in equilibrium thermal fluctuations as the origin of static microinhomogeneities (MIH) in glasses. MIH of compositions seem to be the main source of scattering, and the calculations are found to be in qualitative agreement with both SAXS and RMB measurements. Glasses with PbO content above 40 mol.% are more homogeneous than ideal solutions of PbO and SiO2 whereas MIH in glasses with smaller PbO content are comparable with those expected for ideal solutions of PbO and SiO2. In the latter range SAXS measurements indicate the existence of medium-range order with correlation length of 5-7 Angstrom. (C) 1999 American Institute of Physics. [S0021-9606(99)70409-5].