Structural changes and anomalous self‐diffusion of oxygen in liquid iron at high pressure. Issue 8 (22nd April 2017)

• Record Type: Journal Article
• Authors: Posner, Esther S.; Steinle‐Neumann, Gerd; Vlček, Vojtěch; Rubie, David C.
• Is Part Of: Geophysical research letters. Volume 44:Issue 8(2017)
• Page Start: 3526
• Page End: 3534
• Publication Date: 2017-04-22
• Subjects: oxygen in liquid iron -- structural properties -- diffusion -- outer core; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL072926
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We report structural properties and diffusivity of liquid Fe0.96 O0.04 over a density range of 5.421–11.620 g cm −3, corresponding to pressures of 0–330 GPa and 2200–5500 K, using first‐principles molecular dynamics. We predict a change in compression mechanism near 8 g cm −3 . At lower density, Fe and O coordinations increase from ~10 to ~13 and ~3 to ~6, respectively, the average Fe–O distance increases from ~1.81 Å to ~1.88 Å, and the Fe–Fe distance remains essentially constant. Calculated oxygen diffusivities, D O, remain constant over the corresponding pressure range, consistent with experiments. For larger densities, interatomic distances and diffusion rates for both species decrease monotonically. Oxygen coordination reaches a maximum of ~8.5 at ~9.4 g cm −3, indicating a local B2 packing for Fe around O under conditions of the Earth's core. The pressure‐induced structural evolution provides an explanation for a previously reported change in pressure dependence of oxygen solubility in liquid iron. Key Points: Molecular dynamic simulations show a structural change in liquid Fe0.96 O0.04 from a bcc‐type to close‐packing at a density near 8 g cm −3 Compression <~8 g cm −3 is accommodated by an increase in Fe and O coordinations, while Fe‐Fe distances stay constant and increase for Fe‐O Oxygen diffusion shows a negligible pressure dependence for densities <~8 g cm −3, but diffusivity decreases normally at higher density