Low viscosity of solid MgO at high pressures and strain rates measured using the laser-driven Richtmyer-Meshkov instability

Solids are often assumed to behave as viscous fluids under high-strain rates. This behavior has been studied experimentally in metals but largely unexplored in brittle ceramic materials. In this study, we present a technique for measuring the viscosity of MgO using time-resolved velocimetry to track the growth rate of a perturbation caused by the Richtmyer-Meshkov instability at the OMEGA EP laser facility. To interpret the results, we use an in-house Eulerian hydrocode to simulate our experiments and model the plastic deformation of solid MgO as a viscous fluid. Results indicate that MgO has a surprisingly low upper bound to its effective viscosity of $\ensuremath{\sim}{10}^{2}\phantom{\rule{0.16em}{0ex}}\mathrm{Pa}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ at $175\ifmmode\pm\else\textpm\fi{}15\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}, \ensuremath{\sim}3500\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and ${10}^{6}\ensuremath{-}{10}^{7}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ strain rate.