Single-crystal elasticity of MgO at high pressure

Abstract

The single-crystal elastic properties of MgO were measured by Brillouin scattering in diamond anvil cell to 18.6 GPa. These measurements demonstrate that quasihydrostatic stress conditions can be obtained in solid pressure medium by thermal annealing, and establish the accuracy with which elastic moduli can be measured over this extensive pressure range (\ifmmode\pm\else\textpm\fi{}5% in ${\mathrm{dC}}_{\mathrm{ij}}/dP).$ The acoustic anisotropy of MgO decreases with pressure, with MgO becoming isotropic at \ensuremath{\sim}21.5 GPa. Deviations from noncentral interatomic forces, as measured by the Cauchy relations, increase steadily with pressure.