Optical, mechanical, and elastic response of MgO shock-compressed to 150 GPa

Magnesium oxide (MgO) is an archetypal ionic solid and is a compositional endmember of the ferropericlase solid solution. While recent advances have been made to measure sound speeds under static compression at 300 K using light scattering techniques, the direct measurement of the elastic moduli of MgO have been made only to pressures of ~55 GPa. At higher pressures, experimental measurement of the elastic response of MgO has been limited to determination of aggregate moduli only. Measurement of the velocity of release wave propagation into shock-compressed solids provides a method for directly measuring the elastic properties of materials at simultaneous high pressure and temperature conditions, beyond what is achievable with static compression. In this study, we report shock compression results on [100] MgO single crystals to peak stress states up to ~150 GPa. Laser interferometry was used to simultaneously determine the stress-density response and in situ longitudinal sound speeds in MgO. We note two main results from this work: 1) Although a time-dependent loss in optical transmission at 532 nm is observed across the entire stress range explored in this study, MgO maintains optical transparency at 1550 nm. 2) Our measured longitudinal wave speeds are ~12% lower than results from computational studies and extrapolations from static data for the [100] direction yet are consistent with predictions for the Voigt-Reuss-Hill aggregate wave speed.