Structural evolution of iron oxides melts at Earth’s outer-core pressures
Nature Communications Springer Nature (2026)
Authors:
Céline Crépisson, Mila Fitzgerald, Domenic Peake, Patrick G 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, Phani S Karamched, Zuzana Konôpková, 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
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 177-440 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 177 GPa ( ~ 380 km below the core-mantle boundary) and 3800 K, 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.
