Time resolved X-ray diffraction studies on the non-equilibrium structural dynamics of silicate glasses at ultrahigh pressures

Shock experiments give a unique insight into the behavior of the matter subjected to extreme conditions and are key to modeling material failure and deformation dynamics under ballistic impact. To understand the role of glass network structure on the dynamic response of silicates, we performed laser-driven shock compression experiments on soda-lime glass (SLG) and borosilicate glass (BSG). In-situ VISAR and XRD were used to determine the pressure and structural phases, respectively. Following laser shock compression, between 40-90 GPa, SLG was seen to undergo a poly-amorphic transition from its ambient 4-fold coordinated amorphous structure to a 6-fold coordinated high-density amorphous (HDA) structure. Above 150 GPa, SLG transforms into a high-density melt. Time-resolved in-situ XRD also revealed that a small volume of crystalline d-niccolite phase was formed in the SLG during release between 55 - 80 GPa. In contrast, BSG was seen to transition from its ambient 4-fold amorphous structure to a crystalline stishovite structure in the 40 to 60 GPa range. A mixed phase was observed between 60-70 GPa with HDA and crystalline d-niccolite phases. Above 70 GPa, BSG transforms to HDA followed by high-density melt like that observed in SLG. A pressure-temperature and pressure-time phase diagram was created to describe the structural phases observed. Our in-situ XRD studies were able to directly resolve the structural transformation in silicate glasses and clarify the role of composition.