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

Abstract

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 ∼1.61 at inner core conditions, although the effect of small amount of light elements remains to be examined by experiments.