Chapter 14 - Silicate Glasses Under Ultrahigh Pressure Conditions

Abstract

Despite immense progress in understanding the nature of silicate glasses at high-pressure conditions over the past decade, their atomic structures under ultrahigh pressure above ∼100GPa have yet to be uncovered. This chapter discusses possible structural changes in silicate glasses under ultrahigh pressures, highlighting the recent experimental progress in in situ high-pressure Brillouin scattering spectroscopy. We identified the anomalous increase in the acoustic wave velocity gradients with pressure of SiO2, MgSiO3, and Al2O3–SiO2 glasses above 100GPa. This pressure-induced acoustic wave velocity evolution most likely corresponds to the onset of structural densification associated with an increase in Si–O coordination number from sixfold to a higher coordination state, which might affect the densification mechanisms of the “ultra-deep” magmas in the Earth.