The Effect of Fe‐Al Substitution on the Crystal Structure of MgSiO ₃ Bridgmanite

The crystal chemistry of ten well-characterized bridgmanite single-crystals with Fe and Al contents ranging from 0 to 0.40 atoms per two-cation formula units were investigated by single-crystal X-ray diffraction. Structural refinements indicate that Fe3+ mainly occupy the Mg Si sites, respectively, when present in similar proportions. Molar volumes endmember components refined using data this previous studies found decrease order Fe3+Fe3+O3 > MgFe3+O2.5 Fe3+AlO3 MgAlO2.5 AlAlO3 Fe2+SiO3 MgSiO3. charge-coupled substitution leads an anisotropic increase B-O bond distances, resulting more distorted octahedral B sites a significant c-axis respect a- b-axes. Valence calculations A site is compressible than for all samples studied, implying tilting distortion will dominate compression mechanism. Guided these chemical observations, bulk moduli estimated results studies. volume changes equilibria controlling speciation then calculated at conditions relevant top Earth's lower mantle. proportion oxygen vacancy predicted pressure. While stability component drive charge disproportionation produce iron metal mantle, appears be much less favorable 50 GPa. An component, however, may favor formation higher pressures.