Bridgmanite may contain a large proportion of ferric iron in its crystal structure in the forms of FeFeO₃ and MgFeO_2.5 components. We investigated the pressure dependence of FeFeO₃ and MgFeO_2.5 contents in bridgmanite coexisting with MgFe₂O₄-phase and with or without ferropericlase in the MgO-SiO₂-Fe₂O₃ ternary system at 2,300 K, 33 and 40 GPa. Together with the experiments at 27 GPa reported in Fei et al. (2020, https://doi.org/10.1029/2019GL086296), our results show that the FeFeO₃ and MgFeO_2.5 contents in bridgmanite decrease from 7.6 to 5.3 mol % and from 2 to 3 mol % to nearly zero, respectively, with increasing pressure from 27 to 40 GPa. Accordingly, the total Fe³⁺ decreases from 0.18 to 0.11 pfu. The formation of oxygen vacancies (MgFeO_2.5 component) in bridgmanite is therefore dramatically suppressed by pressure. Oxygen vacancies can be produced by ferric iron in Fe³⁺-rich bridgmanite under the topmost lower mantle conditions, but the concentration should decrease rapidly with increasing pressure. The variation of oxygen-vacancy content with depth may potentially affect the physical properties of bridgmanite and thus affect mantle dynamics.

中文翻译：

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压力使布里奇曼石中的氧空位不稳定

Bridgmanite在其晶体结构中可能包含大量FeFeO ₃和MgFeO _2.5成分形式的三价铁。我们研究了在 2,300 K、33 和 40 GPa 条件下，在 MgO-SiO ₂ -Fe ₂ O ₃三元体系中与 MgFe ₂ O ₄相共存且有或没有铁方镁石的桥锰矿中 FeFeO ₃和 MgFeO _2.5含量的压力依赖性。连同 Fei 等人报道的 27 GPa 实验。(2020, https://doi.org/10.1029/2019GL086296)，我们的结果表明 FeFeO ₃和 MgFeO _2.5随着压力从 27 GPa 增加到 40 GPa，布里奇曼石中的含量分别从 7.6 至 5.3 mol % 和从 2 至 3 mol % 降至几乎为零。因此，总 Fe ³⁺从 0.18 pfu 减少到 0.11 pfu。因此，桥锰矿中氧空位（MgFeO _2.5组分）的形成被压力显着抑制。氧空位在下地幔顶部条件下富Fe ³⁺桥锰矿中的三价铁可以产生氧空位，但随着压力的增加，氧空位浓度会迅速下降。氧空位含量随深度的变化可能会影响布里奇曼石的物理性质，从而影响地幔动力学。