The solubility of the MgAlO_{2.5} component in bridgmanite was measured at pressures of 27, 35 and 40 GPa and a temperature of 2000 K. Compositional analysis of recovered samples demonstrated that the MgAlO_{2.5} component decreases with increasing pressure, and approaches virtually zero at 40 GPa. Above this pressure, the MgAlO_{2.5} component, i.e., the oxygenvacancy substitution, becomes negligible, and Al is incorporated in bridgmanite by the chargecoupled substitution only.

Fig. 1.
The oxygen number to the bridgmanite unit formula, which should be 3 if the MgAlO_{2.5} content is zero. The oxygen number becomes virtually zero at pressures above 40 GPa.
Liu, Z., Ishii, T., Katsura, T. (2017) Rapid decrease of MgAlO_{2.5} component in bridgmanite with pressure. Geochem. Persp. Let. 5, 12–18.