Structural evolution of iron oxides melts at Earth’s outer-core pressures
- 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 Konopkova
- 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
2026-07-10
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 Fe 2 O 3 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 Fe 2 O 3 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, Fe 2 O 3 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.