Effect of chemistry on the stability and elasticity of the perovskite and post-perovskite phases in the MgSiO3-FeSiO3-Al2O3 system and implications for the lowermost mantle

摘要

Using first-principles calculations we predict the effects of composition on the perovskite to post-perovskite phase transition. The transition is predicted at 107 GPa for pure MgSiO3. The addition of Al2O3 slightly increases this transition pressure, and the addition of Fe2+ considerably reduces it; the FeSiO3 end-member term is stable in the post-perovskite modification with respect to perovskite at all pressures. We also determine the static equations of state, densities, elasticity and seismic wave velocities. At the transition V-p increases slightly, and Vs increases significantly, consistent with the seismic observations for D ''. The addition of both Fe2+ and Al2O3 decrease the seismic wave velocities.