Influence of Pressure-Induced Structural Change in Al2O3-SiO2 Glasses on the Sound Velocity and Poisson's Ratio under Pressure

In this study, we investigated pressure-induced changes in the structure and elastic properties of xAl2O3-(100 - x)SiO2 glasses (x = 29, 36, 43, 50, 60 mol%; referred to as xAS) by in situ high-pressure pair distribution function measurement and sound velocity measurement. The 29AS and 60AS glasses are regarded as Si-rich/Al-rich end-member compositions, and the 36AS, 43AS, and 50AS glasses consist of the two end-member phases at the nanoscale. The 29AS glass shows gradual changes in the intermediate-range order up to 9.3 GPa, similar to SiO2 glass, while the 60AS glass exhibits a rapid structural change at 7.4-8.4 GPa, similar to CaAl2O4 glass. This rapid structural change causes a kink in the sound velocity-pressure trend near 8 GPa, as also observed in CaAl2O4 glass. In contrast, the Si-rich end-member 29AS glass does not exhibit the velocity kink. The Poisson's ratios of the five AS glasses and the SiO2 glass start to converge above similar to 11 GPa, finally reaching a constant value of similar to 0.32 at a pressure of similar to 20 GPa. This result indicates that both the Si-rich and Al-rich end-members have a similar structure above similar to 20 GPa.