The structure of Fe-Ni alloy in Earth's inner core

The crystal structure of Fe-10%Ni was investigated up to 340 GPa and 4700 K, corresponding to the Earth's inner core conditions by synchrotron X-ray diffraction measurements in-situ at ultrahigh pressure and temperature in a laser-heated diamond-anvil cell. The results show that hexagonal closed-packed (hcp) structure is stable throughout the experimental conditions investigated with no evidence for a phase transition to body-centered cubic (bcc) or face-centered cubic (fcc) phases. The axial c/a ratio of the hcp crystal obtained around 330 GPa has a small temperature dependence similar to the axial ratio of pure Fe. Iron alloy with less than 10% Ni crystallizes to an hcp structure with c/a ratio of similar to 1.61 at inner core conditions, although the effect of small amount of light elements remains to be examined by experiments. Citation: Tateno, S., K. Hirose, T. Komabayashi, H. Ozawa, and Y. Ohishi (2012), The structure of Fe-Ni alloy in Earth's inner core, Geophys. Res. Lett., 39, L12305, doi:10.1029/2012GL052103.