Study of iron oxides in amorphous and molten phases under laser-driven shock compression at Earth's outer-core pressure conditions
ORAL · Invited
Abstract
The iron-rich outer core of the Earth contains up to 5% oxygen. The study of iron oxide melts is thus of importance for the understanding of the Fe-O bonding environment in this region. Changes in Fe-O bonding have been proposed to be at the origin of a possible layering in the middle of the Earth’s outer-core (Ozawa et al., Science, 2011). Seismological observations also suggest a stratification, at the top of the Earth’s outer core, which is highly relevant to better understand the geodynamo.
We present here new experimental results based on three different experiments on Fe60O40 and Fe2O3 under laser-driven shock compression at an x-ray free electron laser. In-situ melting and structure of the melts were studied via x-ray diffraction for the entire range of pressure conditions present in the Earth’s outer-core (136 to 330 GPa).
Fe2O3 is shown to undergo amorphization around 120 GPa (Crepisson et al., PRB, 2025) and insight into the amorphization process is provided from study of the remaining high-pressure phase. Melting occurs above around 150 GPa for Fe2O3. Liquid signal and its evolution upon increasing pressure reveals interesting and unexpected features. Indeed, two liquid diffraction peaks are observed, their positions shift slightly toward higher scattering vectors while their relative intensities vary significantly with pressure. Fully molten Fe60O40 is observed at around 180 GPa and the retrieved liquid signals present a more common evolution with one diffraction peak shifting steadily toward higher scattering vector with increasing pressure.
Careful corrections of the x-ray diffraction signal are performed to carry out liquid diffraction analysis. Preliminary pair distribution function and melt structure along the shock Hugoniot are presented, based on the method developed in Eggert et al., PRB, 2002. Implications for planetary science and the Earth’s outer-core are discussed.
We present here new experimental results based on three different experiments on Fe60O40 and Fe2O3 under laser-driven shock compression at an x-ray free electron laser. In-situ melting and structure of the melts were studied via x-ray diffraction for the entire range of pressure conditions present in the Earth’s outer-core (136 to 330 GPa).
Fe2O3 is shown to undergo amorphization around 120 GPa (Crepisson et al., PRB, 2025) and insight into the amorphization process is provided from study of the remaining high-pressure phase. Melting occurs above around 150 GPa for Fe2O3. Liquid signal and its evolution upon increasing pressure reveals interesting and unexpected features. Indeed, two liquid diffraction peaks are observed, their positions shift slightly toward higher scattering vectors while their relative intensities vary significantly with pressure. Fully molten Fe60O40 is observed at around 180 GPa and the retrieved liquid signals present a more common evolution with one diffraction peak shifting steadily toward higher scattering vector with increasing pressure.
Careful corrections of the x-ray diffraction signal are performed to carry out liquid diffraction analysis. Preliminary pair distribution function and melt structure along the shock Hugoniot are presented, based on the method developed in Eggert et al., PRB, 2002. Implications for planetary science and the Earth’s outer-core are discussed.
*We acknowledge UK EPSRC under grants EP/P015794/1, EP/W010097/1and EP/X031624/1.
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Publication: Crepisson et al., Phys. Rev. B 111, 024209, 2025 https://doi.org/10.1103/PhysRevB.111.024209
Amouretti et al.under review for Phys. Rev. L., arXiv https://doi.org/10.48550/arXiv.2402.18432
Presenters
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Celine Crepisson
- Physics Department University of Oxford
- University of Oxford