Structural properties of Fe1-xNix compressed and heated to the Earth's core conditions

• Cosmochemical, geochemical, and geophysical studies provide evidences that Earth's core contains iron with substantial (5 to 15 at. %) amounts of nickel and/or impurities of light elements. The results of our combined first-principles study and in-situ and temperature-quenched laser-heated diamond anvil-cell experiments on the high-pressure high-temperature structural behavior of pure Fe and Fe_0.9 Ni_0.1 alloy are reported. Our temperature-quenched experiments indicate that the face-centered cubic (fcc) phase of pure iron can exist in the pressure-temperature region above 160 GPa and 3700 K. In accord our theoretical results show that the fcc phase of Fe becomes as stable as the hexagonal-close-packed (hcp) phase at Earth's core condition (P ~ 300-360 GPa and T around 5000-6000 K). Further we demonstrate by means of in-situ angle-dispersive x-ray diffraction in internally heated diamond anvil cells (DACs) that by substantial alloying of Fe with Ni (10 at. %) a body-centered cubic phase can stabilize in the Earth's core. Our results give an evidence that the actual structure of the the Earth's core could be a complex phase, which is very sensitive to the presence of impurities of nickel, sulfur, silicon, etc. 

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