Thermoelasticity of MgO up to 400 GPa using shock-ramp compression on the Z machine

Periclase (MgO) is a common thermodynamic pressure standard and widely used in developing new techniques in high pressure science. MgO is also the major component of the mineral ferropericlase (Mg,Fe)O, the most abundant non-silicate oxide mineral in Earth’s lower mantle. As a prevalent lower mantle mineral stable at the core-mantle boundary (CMB), determining the thermoelastic properties of MgO at CMB conditions is essential to benchmarking compositional and thermal models of the Earth’s interior. Using standard-width stripline targets on the Z machine at Sandia National Laboratories, we shocked polycrystalline MgO up to 100 and 150 GPa using Al flyers in separate experiments, from which quasi-isentropic ramp compressions were applied up to ~400 GPa with pulse shaping. We obtained thermoelastic results along the elevated quasi-isentropes spanning pressures of 100-400 GPa. Complementary ab-initio calculations incorporating strength estimates show good agreement with the experimental data and provide an independent validation of the methodology. In addition, we obtained an uncertainty aware bulk sound velocity of MgO along the ramps using inverse Lagrangian analyses. Sound velocity is an essential parameter for interpreting the seismic structure of Earth’s core-mantle boundary region.