Micro- and nanoinhomogenities in glasses and their melts studied by optical, SAXS, acoustical and thermodynamic methods

Abstract

Ultrasonic waves velocities are studied in glasses of the systems Na2O - GeO2 and K2O - GeO2 and in glasses and melts of the system PbO-GeO2. Our Rayleigh-Mandelshtam-Brillouin light scattering (RMBS), small angle X-ray scattering (SAXS) and Raman scattering (RS) experimental data for glasses of the system PbO-GeO2 have been analyzed. At small concentrations of metallic oxides a ‘‘water-like anomaly’’ is observed, i.e. the increase of sound velocity with raising temperature. The results of scattering are compared with calculations based on the concept of ‘‘frozen-in’’ equilibrium thermal fluctuations as the origin of static inhomogeneities in glasses. Discussion of glass composition dependences of the data obtained was performed in terms of ‘‘freezing’’ equilibrium thermodynamic fluctuations of density and concentration (chemical composition) in a glass melt at the process of its cooling and transformation into solid state. Usage of acoustic and electrochemical data for glass melts makes it possible to estimate contributions of ‘‘frozen-in’’ density and concentration fluctuations into Rayleigh scattering losses separately. Combining RMBS and RS data gave the answer to the important question: concentration of which structural species fluctuates in a glass melt? It was found that RS spectra of glasses contain information about units of a glass - groups with constant stoichiometry. These groups are characterized by components of the RS spectra intensities of which correspond with concentration of these groups. It means that some multicomponent glasses built from the groups of a single type. As a rule, these glasses are characterized by high level of chemical (and optical) homogeneity