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

Iuliia Koemets; Biao Wang; Egor Koemets; Takayuki Ishii; Zhaodong Liu; Catherine McCammon; Artem Chanyshev; Tomo Katsura; Michael Hanfland; Alexander Chumakov; Leonid Dubrovinsky

doi:10.3389/fchem.2023.1258389

Crystal chemistry and compressibility of Fe_0.5Mg_0.5Al_0.5Si_0.5O₃ and FeMg_0.5Si_0.5O₃ silicate perovskites at pressures up to 95 GPa

Front Chem. 2023 Oct 6:11:1258389. doi: 10.3389/fchem.2023.1258389. eCollection 2023.

Authors

Affiliations

¹ Bayerisches Geo Institute (BGI), Universität Bayreuth, Bayreuth, Germany.
² Department of Earth Sciences, University of Oxford, Oxford, United Kingdom.
³ Institute for Planetary Materials, Okayama University, Misasa, Japan.
⁴ State Key Laboratory of Superhard Materials, Jilin University, Changchun, China.
⁵ European Synchrotron Radiation Facility (ESRF), Grenoble, France.

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, FeMg_0.5Si_0.5O₃ and Fe_0.5Mg_0.5Al_0.5Si_0.5O₃, 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 FeMg_0.5Si_0.5O₃ phase adopts a novel monoclinic double-perovskite structure with the space group of P21/n at pressures above 12 GPa, whereas the Fe_0.5Mg_0.5Al_0.5Si_0.5O₃ 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 (Fe_0.7,Mg_0.3)O₆ octahedral site of the FeMg_0.5Si_0.5O₃ phase at pressures higher than 40 GPa. No iron spin transition was observed for the Fe_0.5Mg_0.5Al_0.5Si_0.5O₃ phase as all Fe³⁺ ions are located in bicapped prism sites, which have larger volumes than an octahedral site of (Al_0.5,Si_0.5)O₆.

Keywords: bridgmanite; double perovskite; high pressure; silicate perovskite; single-crystal X-ray diffraction; spin transition; synchrotron Mössbauer spectroscopy.

Grants and funding

The authors declare that financial support was received for the research, authorship, and/or publication of this article. This work is supported by the Advanced Grant of the European Research Council (ERC) under the Horizon 2020 research and innovation program of the European Union (No. 787527) to TK.