Hugoniot, sound speed, and phase transitions of sapphire for pressures 0.2-2.1 TPa

Sapphire (Al₂O₃) is important to high-pressure physics and understanding the interiors of Earth-like planets. In high-pressure physics, it is commonly used in it’s Cr-doped form, ruby, as a pressure standard for diamond anvil cells. In planetary physics, it is one of the end-member constituents of the mantle. Its properties are poorly known for pressures >350 GPa, and the pressures at which the various solid-solid phase transitions and shock melting occur have not been fully constrained. We present a wide-range sapphire Hugoniot covering the pressure range 0.2-2.1 TPa and identify pressures where the principal Hugoniot intersects solid-solid phase boundaries and the melt curve. Sound speeds were measured in both solid and liquid material to help constrain off-Hugoniot properties of the material. A multiphase Hugoniot fit was determined and can be used for future high-pressure experiments using sapphire as an equation of state standard.