Structural evolution of iron oxides melts at Earth's outer-core pressures
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.
Cite
@article{arxiv.2511.20144,
title = {Structural evolution of iron oxides melts at Earth's outer-core pressures},
author = {Céline Crépisson and Mila Fitzgerald and Domenic Peake and Patrick Heighway and Thomas Stevens and Adrien Descamps and David McGonegle and Alexis Amouretti and Karim K. Alaa El-Din and Michal Andrzejewski and Sam Azadi and Erik Brambrink and Carolina Camarda and David A. Chin and Samuele Di Dio Cafiso and Ana Coutinho Dutra and Hauke Höppner and Kohdai Yamamoto and Zuzana Konôpkovà and Motoaki Nakatsutsumi and Norimasa Ozaki and Danae N. Polsin and Jan-Patrick Schwinkendorf and Georgiy Shoulga and Cornelius Strohm and Minxue Tang and Harry Taylor and Monika Toncian and Yizhen Wang and Jin Yao and Gianluca Gregori and Justin S. Wark and Karen Appel and Marion Harmand and Sam M. Vinko},
journal= {arXiv preprint arXiv:2511.20144},
year = {2025}
}
Comments
14 pages, 7 figures, under review