Structural evolution of iron oxides melts at Earth's outer-core pressures

Céline Crépisson; Mila Fitzgerald; Domenic Peake; Patrick Heighway; Thomas Stevens; Adrien Descamps; David McGonegle; Alexis Amouretti; Karim K. Alaa El-Din; Michal Andrzejewski; Sam Azadi; Erik Brambrink; Carolina Camarda; David A. Chin; Samuele Di Dio Cafiso; Ana Coutinho Dutra; Hauke Höppner; Kohdai Yamamoto; Zuzana Konôpkovà; Motoaki Nakatsutsumi; Norimasa Ozaki; Danae N. Polsin; Jan-Patrick Schwinkendorf; Georgiy Shoulga; Cornelius Strohm; Minxue Tang; Harry Taylor; Monika Toncian; Yizhen Wang; Jin Yao; Gianluca Gregori; Justin S. Wark; Karen Appel; Marion Harmand; Sam M. Vinko

arXiv · 2511.20144

Structural evolution of iron oxides melts at Earth's outer-core pressures

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Abstract

Oxygen and other light elements comprise up to 5 wt% of the Earth's outer-core, and may significantly influence its physical properties and the operation of the geodynamo. Here we report in situ x-ray diffraction measurements of Fe, Fe + 4.5 FeO (atomic proportion), and Fe2O3 melts at 177-438 GPa, achieved using laser-driven shock compression at an x-ray free-electron laser. The melts exhibit Fe-O coordination numbers between 4.0(0.4) and 4.5(0.4), indicating predominantly four-fold coordination environments. These coordination states are significantly smaller than those of Fe-bearing lower-mantle phases such as bridgmanite and ferropericlase. Shorter Fe-Fe interatomic distances in compressed iron oxide melts drive the denser packing relative to ambient melts, while the structural differences between Fe + 4.5 FeO and Fe2O3 melts under shock indicate that the oxidation state modulates oxygen solubility in liquid Fe. At around 177 GPa (380 km below the core-mantle boundary), Fe2O3 melts exhibit higher Fe-O coordination, suggesting that local variations in oxygen content could contribute to the stratification in the uppermost outer-core inferred from seismological and geomagnetic observations.

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Céline Crépisson, Mila Fitzgerald, Domenic Peake, Patrick Heighway, Thomas Stevens, Adrien Descamps, David McGonegle, Alexis Amouretti, Karim K. Alaa El-Din, Michal Andrzejewski, Sam Azadi, Erik Brambrink, Carolina Camarda, David A. Chin, Samuele Di Dio Cafiso, Ana Coutinho Dutra, Hauke Höppner, Kohdai Yamamoto, Zuzana Konôpkovà, Motoaki Nakatsutsumi, Norimasa Ozaki, Danae N. Polsin, Jan-Patrick Schwinkendorf, Georgiy Shoulga, Cornelius Strohm, Minxue Tang, Harry Taylor, Monika Toncian, Yizhen Wang, Jin Yao, Gianluca Gregori, Justin S. Wark, Karen Appel, Marion Harmand, Sam M. Vinko. 2025-11-25. Structural evolution of iron oxides melts at Earth's outer-core pressures. https://arxiv.org/abs/2511.20144

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