Sound velocity of hexagonal close-packed iron to the Earth's inner core pressure

Here we determine the compressional and shear wave velocities (v(p) and v(s)) of hexagonal close-packed iron, a candidate for the main constituent of the Earth's inner core, to pressures above 300 gigapascals using a newly designed diamond anvil cell and inelastic X-ray scattering combined with X-ray diffraction. The present results reveal that the v(p) and v(s) of the Preliminary reference Earth model (PREM) inner core are 4(+/- 2)% and 36(+/- 17)% slower than those of the pure iron, respectively at the centre of the core. The density and sound velocity of the PREM inner core can be explained by addition of 3(+/- 1) wt% silicon and 3(+/- 2) wt% sulphur to iron-5 wt% nickel alloy. Our suggested inner core composition is consistent with the existing outer core model with oxygen, as the growth of the inner core may have created a secular enrichment of the element in the outer core. New constraints on the composition of Earth's inner core are provided by experimental verification of Birch's law for hexagonal close-packed iron to pressure above 300 gigapascals, about double the pressure achieved in previous investigations

Automated summary

In this study, the compressional and shear wave velocities of hexagonal close-packed iron were determined at high pressures, providing insights into the composition and evolution of Earth's inner core. The results suggest that the inner core of the Earth is slower in terms of wave velocities compared to pure iron, with the addition of silicon and sulfur to the iron-nickel alloy explaining the observed density and sound velocity. These findings contribute to a better understanding of the Earth's core composition.