Study of the dynamic compression response of SiO₂ to Mbar pressures using in-situ femtosecond X-ray diffraction and <i>ab initio</i> simulations

We investigated the high-pressure behavior of SiO₂ which is of great interest to planetary- and material science, as it is a major phase constituent in the Earth's mantle and widely used as standard material in shock compression experiments. The high-pressure phase transformations of quartz, observed in static and dynamic (shock) compression experiments, are contradicting and questions remain about the effect of compression rate on the structural response. We performed time-resolved X-ray diffraction studies at 15 - 130 GPa, using the dynamics compression platform at the MEC end-station of the Linac Coherent Light Source. Our study mainly focused on the in situ time-resolved structural transformation of quartz on its respective Hugoniot and reaching temperatures corresponding to the SiO₂-liquidus regime.
While simultaneously probing the samples with highly resolved X-ray diffraction at various time delays, it was possible to obtain time-resolved information of the lattice structure during phase transitions, melting and re-crystallization of SiO₂. The experimental conditions could be reproduced by ab initio simulations which gave further insights into the phase transition.