Static compression of Fe0.83Ni0.09Si0.08 alloy to 374 GPa and Fe0.93Si0.07 alloy to 252 GPa: Implications for the Earth's inner core

The pressure–volume equations of state of iron–nickel–silicon alloy Fe0.83Ni0.09Si0.08 (Fe-9.8 wt.% Ni-4.0 wt.% Si) and iron–silicon alloy Fe0.93Si0.07 (Fe-3.4 wt.% Si) have been investigated up to 374 GPa and 252 GPa, respectively. The present compression data covered pressures of the Earth's core. We confirmed that both Fe0.83Ni0.09Si0.08 and Fe0.93Si0.07 alloys remain in the hexagonal close packed structure at all pressures studied.We obtained the density of these alloys at the pressure of the inner core boundary (ICB), 330 GPa at 300 K by fitting the compression data to the third order Birch–Murnaghan equation of state. Using these density values combined with the previous data for hcp-Fe, hcp-Fe0.8Ni0.2, and hcp-Fe0.84Si0.16 alloys and comparing with the density of the PREM inner core, we estimated the Ni and Si contents of the inner core. The Si content of the inner core estimated here is slightly greater than that estimated previously based on the sound velocity measurement of the hcp-Fe–Ni–Si alloy at high pressure.

:
► We report that Fe0.83Ni0.09Si0.08 alloy remains as an hcp structure to 374 GPa.
► Fe0.93Si0.07 alloy possesses the same structure to 252 GPa.
► We determined the compression curves of these Fe–Ni–Si alloys to the core pressures.
► Our results revealed that the inner core contains 7.5 to 11 at % silicon.