Étude des propriétés élastiques des verres d’oxydes sous haute pression : implications structurales

The structural study of glasses under pressure is of fundamental interest in Physics, Earth Science and is technologically important for the comprehension of industrial material properties. The elastic anomaly at 2.5GPa in pure silica glass is a well known phenomenon and its existence is more than likely in GeO2 glass. In this work the persistence of the elastic anomaly in more complex and more widely glass compositions as sodium alumino silicate glasses was studied. The elastic anomaly was studied in situ in GeO2 and three sodium alumino silicate glasses by Brillouin and Raman scattering. The studied sodium alumino silicate glasses had the following compositions : (Al2O3)X(Na2O)25-X(SiO2)75 where X=0, 6 et 12% and is the molar percentage of Al2O3. The elastic anomaly was shown to persist in a broad domain of chemical compositions thus its existence is not reduced to pure silica glass. Its existence seems to be linked to the presence of 6 membered rings. Beyond the elastic limit, the structural modifications was studied in pure silica, GeO2 glass and sodium alumino silica glasses (with X=0, 2, 6, 9, 12 et 16% of Al2O3) in order to structurally better understand the densification phenomenon. Firstly the elastic anomaly was studied by Brillouin scattering experiments, was shown to progressively disappear with the densification. This progressive disappearance was interpreted in terms of a progressive structure induced transformation from a Low Density Amorphous form (LDA) into a High Density Amorphous form (HDA). In situ and ex situ studies by Brillouin and Raman scattering, Nuclear Magnetic Resonance (NMR) and X-ray Absorption Near Edge Structure (XANES) showed that the pressure induced structural transformation was highly dependent of the glass chemical composition. For instance the presence of sodium cations promotes short range order modifications, such as formation of highly coordinated species (Al, Si) and network depolymerization. On the other hand, glasses with a high aluminum concentration show a densification process closer to that of pure silica glass, with mainly middle range order structural modifications such as a decrease of the inter-tetrahedral angle or ring size decrease. The structural study of glasses under pressure is of fundamental interest in Physics, Earth Science and is technologically important for the comprehension of industrial material properties. The elastic anomaly at 2.5GPa in pure silica glass is a well known phenomenon and its existence is more than likely in GeO2 glass. In this work the persistence of the elastic anomaly in more complex and more widely glass compositions as sodium alumino silicate glasses was studied. The elastic anomaly was studied in situ in GeO2 and three sodium alumino silicate glasses by Brillouin and Raman scattering. The studied sodium alumino silicate glasses had the following compositions : (Al2O3)X(Na2O)25-X(SiO2)75 where X=0, 6 et 12% and is the molar percentage of Al2O3. The elastic anomaly was shown to persist in a broad domain of chemical compositions thus its existence is not reduced to pure silica glass. Its existence seems to be linked to the presence of 6 membered rings. Beyond the elastic limit, the structural modifications was studied in pure silica, GeO2 glass and sodium alumino silica glasses (with X=0, 2, 6, 9, 12 et 16% of Al2O3) in order to structurally better understand the densification phenomenon. Firstly the elastic anomaly was studied by Brillouin scattering experiments, was shown to progressively disappear with the densification. This progressive disappearance was interpreted in terms of a progressive structure induced transformation from a Low Density Amorphous form (LDA) into a High Density Amorphous form (HDA). In situ and ex situ studies by Brillouin and Raman scattering, Nuclear Magnetic Resonance (NMR) and X-ray Absorption Near Edge Structure (XANES) showed that the pressure induced structural transformation was highly dependent of the glass chemical composition. For instance the presence of sodium cations promotes short range order modifications, such as formation of highly coordinated species (Al, Si) and network depolymerization. On the other hand, glasses with a high aluminum concentration show a densification process closer to that of pure silica glass, with mainly middle range order structural modifications such as a decrease of the inter-tetrahedral angle or ring size decrease.

Keywords: Brillouin scattering
High pressure
Oxide glass
Raman scattering
silica
XANES
Advisor: Henderson, Grant S
Mermet, Alain