AN ANALYSIS OF IN SITU X-RAY DIFFRACTION OF SIO2 UNDER SHOCK COMPRESSION

Abstract

SiO2 is one of the most intensely studied materials under high pressure conditions due to the ubiquity of silicates in Earth’s crust and serves as an important analog for crustal silicates. There has been extensive study of SiO2 under both static and shock compression, but there is still debate on the nature of phase transition(s) that occur in shock compression experiments. In this study data are analyzed from in situ X-ray diffraction probes of SiO2 (novaculite) subjected to laser-driven shock compression at the Matter in Extreme Conditions (MEC) end station of the Linac Coherent Light Source (LCLS). We find distinct evidence for phase transition in several experimental runs. The high-pressure phase stishovite is found to be a poor match for the observed phase, as is the metastable d-NiAs-type phase of SiO2, although stronger evidence for this phase exists as compared to stishovite. There is likely significant formation of an amorphous glass phase of SiO2, although this does not explain all observed features. Further work is needed to better constrain and characterize observed phase transitions.