Crystal chemistry and compressibility of Fe₀.₅Mg₀.₅Al₀.₅Si₀.₅O₃ and FeMg₀.₅Si₀.₅O₃ silicate perovskites at pressures up to 95 GPa

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Koemets, Iuliia ; Wang, Biao ; Koemets, Egor ; Ishii, Takayuki ; Liu, Zhaodong ; McCammon, Catherine ; Chanyshev, Artem ; Katsura, Tomoo ; Hanfland, Michael ; Chumakov, Alexander ; Dubrovinsky, Leonid:
Crystal chemistry and compressibility of Fe₀.₅Mg₀.₅Al₀.₅Si₀.₅O₃ and FeMg₀.₅Si₀.₅O₃ silicate perovskites at pressures up to 95 GPa.
In: Frontiers in Chemistry. Bd. 11 (2023) . - 1258389.
ISSN 2296-2646
DOI: https://doi.org/10.3389/fchem.2023.1258389

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Abstract

Silicate perovskite, with the mineral name bridgmanite, is the most abundant mineral in the Earth’s lower mantle. We investigated crystal structures and equations of state of two perovskite-type Fe3+-rich phases, FeMg0.5Si0.5O3 and Fe0.5Mg0.5Al0.5Si0.5O3, at high pressures, employing single-crystal X-ray diffraction and synchrotron Mössbauer spectroscopy. We solved their crystal structures at high pressures and found that the FeMg0.5Si0.5O3 phase adopts a novel monoclinic double-perovskite structure with the space group of P21/n at pressures above 12 GPa, whereas the Fe0.5Mg0.5Al0.5Si0.5O3 phase adopts an orthorhombic perovskite structure with the space group of Pnma at pressures above 8 GPa. The pressure induces an iron spin transition for Fe3+ in a (Fe0.7,Mg0.3)O6 octahedral site of the FeMg0.5Si0.5O3 phase at pressures higher than 40 GPa. No iron spin transition was observed for the Fe0.5Mg0.5Al0.5Si0.5O3 phase as all Fe3+ ions are located in bicapped prism sites, which have larger volumes than an octahedral site of (Al0.5,Si0.5)O6.