X-ray study of lithium disilicate glass: High pressure densification and polyamorphism

We have investigated the structural changes induced by high-pressure in lithium disilicate glass with stoichiometric composition Li2O.2SiO2 (LS2). Using toroidal type high-pressure chambers, glass samples were processed at 2.5 GPa, 4 GPa, 6 GPa and 7.7 GPa at room temperature. Synchrotron X-ray diffraction measurements were used to obtain the radial distribution functions (RDF) in order to follow the structural changes induced after processing at high pressure. Compared to a pristine sample, the main change observed for the samples processed up to 6 GPa was associated to the distortion of the SiO4 tetrahedral structure. However, for the sample processed at 7.7 GPa, a drastic change in the RDF indicated the formation of a distinct amorphous phase. The observed polyamorphism is important for a better understanding of the nucleation kinetics of crystalline phases under high pressure.