Dynamic Compression of Planetary Materials*

Dynamic compression is a powerful means of studying the physical and chemical properties of materials under extreme conditions on time scales between nano- and micro-seconds. Dynamic compression allows for the study of a broad range of time-dependent condensed matter phenomena, such as structural phase transformations, inelastic deformation, and fracture. Furthermore, dynamic compression has been used to constrain the equation of state of materials to conditions that traditional static-compression techniques cannot reach. Recently, newly developed ramp-loading techniques using high-powered lasers and pulsed-power systems provide access to new regimes of pressure-temperature space. Ramp compression combined with in situ X-ray diffraction allows observation of the structural behavior, phase transitions, and kinetics of planetary materials at extreme conditions.

This talk will summarize our recent studies at the Omega laser and Z facility. At Omega, laser-driven ramp-compression experiments with in situ X-ray diffraction were performed to explore the structural behavior and phase transitions in germanium dioxide, GeO₂. For GeO₂ which serves as an analog for SiO₂, we have examined its crystal structure up to 882 GPa. X-ray diffraction results show that GeO₂ adopts the HP-PdF₂-type structure under ramp loading from 154 GPa to 440 GPa. Above 440 GPa, we observe evidence for a post-HP-PdF₂ phase in GeO₂. The best candidate for this new phase is the cotunnite-type structure. These results offer a test of theoretical calculations as well as insights into the possible high-pressure behavior of SiO₂. At the Z-facility, shock-compression experiments were performed on iron-bearing bridgmanite (Mg_0.92,Fe_0.08)SiO₃ in the range of ~450 GPa to constrain its melting point on the Hugoniot. Our Hugoniot sound velocity measurements will allow for interpreting the melting point of Mg-rich silicates. These experiments will offer insights into impact processes relevant to planetary formation and evolution.