EOS & Thermodynamics of Warm Dense Silica (SiO2) using laser-driven shock compression of Stishovite

Laboratory experiments with laser-driven shocks provide access to explore new regimes of warm dense matter. Due to its high starting density (4.3g/cc), the Hugoniot of Stishovite explores a much denser and cooler path than α-quartz (ρ0=2.65 g/cc) and fuse Silica (ρ0=2.2 g/cc) Hugoniot curves. Stishovite polycrystalline samples and single crystals were synthesized at high pressure-temperature conditions using large-volume-press techniques. The samples were characterized by powder or single-crystal X-ray diffraction, Raman spectroscopy, scanning electron microscopy and wavelength-dispersive X-ray spectroscopy. Their phase and chemical purity was confirmed by appropriate analytical methods. Stishovite poly- and single crystals were shock compressed with direct-drive laser-compression at the Omega Laser Facility in Rochester, NY. We used interferometric Doppler interferometry (VISAR) and streaked optical pyrometry (SOP) with an α-quartz reference. We will discuss optical reflectivity and equation of state (pressure, density, temperature) measurements on warm dense Silica up to ~15 Mbar and 50 000K, compare them with similar measurements on other Silica polymorphs, and explore the consequences for large impact and planetary evolution modeling. In particular, we will show how our data provide a measurement of the melting temperature of SiO2 along the Stishovite Hugoniot, i.e according to a preliminary analysis near 5Mbar and 8500 K.