MR027-08
The fate of iron oxides at multimegabar pressure regime

Wednesday, 16 December 2020: 16:28
Virtual
Saiana Khandarkhaeva1, Timofey Fedotenko2, Elena Bykova3, Maxim Bykov4, Konstantin Glazyrin5, Stella Chariton6, Natalia Dubrovinskaia2 and Leonid S Dubrovinsky7, (1)Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, Germany, (2)Laboratory of Crystallography, Universitaet Bayreuth, Bayreuth, Germany, (3)Carnegie Institution for Science Washington, Earth and Planets Laboratory, Washington, DC, United States, (4)Howard University, Washington, DC, United States, (5)DESY Deutsches Elektronen Synchrotron, Hamburg, Germany, (6)University of Chicago, Center for Advanced Radiation Sources, Chicago, IL, United States, (7)University of Bayreuth, Bayerisches Geoinstitut, Bayreuth, Germany
Recorded Presentation
Abstract:
Discovery and characterization of planets in and beyond the Solar system can have a great impact on science and potentially the cultural image of humanity. By 2020, about 4000 extrasolar planets have been confirmed, whereas some of them have rocky-type composition. (Mg,Fe)(Si,Al)O3 perovskite is supposed to be a key component of super-Earths’ interior. Understanding the fate of perovskite and post-perovskite phases and their assembly at multimegabar pressures is the first step for revealing of the mineralogy of Earth-type exoplanets. Iron oxides, Fe2O3 and Fe3O4, are the end-members of complex silicates solid solutions and could serve as model crystal-chemical analogs of MgSiO3 and Mg2SiO4.

Utilization of laser-heated diamond anvil cells coupled with single crystal X-ray diffraction (SCXRD) is the most efficient way to cover megabar pressures and corresponding temperature regimes with the extraction of unique and unequivocal information of chemistry and atomic structures of new materials.

In the present work, we perform in situ studies of Fe2O3, the simplest crystal chemistry analog of MgSiO3, at ultra-high PT-range. We found that dense η-Fe2O3 (post-perovskite phase) starts to decompose at ~160 GPa and ~3500 K via the formation of complex iron oxides Fe13O19 and Fe19O27, with releasing of oxygen. The end-product of decomposition of η-Fe2O3 in our experiments is Fe3O4 presented by several high pressure modifications. One of them, observed at ~160 GPa has a distorted cubic Th3P4 type of structure which previously hasn’t been detected for any of iron oxide phases. Another two polymorphs of Fe3O4, observed at ~180 GPa, belong to the so-called “post-post-spinel” structure type and have been recently debated in the literature. In our work, we establish their correct space group, atomic arrangement, and chemical composition by means of SCXRD with submicron sized samples.

Our results demonstrate that the behavior of Fe2O3 and Fe3O4 at multimegabar pressures is essential for control the oxygen fugacity in super-Earth mantles and for processes leading to the segregation of metallic cores from oxides/silicate mantles of rocky-type exoplanets.

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