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

Daijo Ikuta; Eiji Ohtani; Hiroshi Fukui; Takeshi Sakai; Daisuke Ishikawa; Alfred Q R Baron

doi:10.1038/s41467-022-34789-2

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

Nat Commun. 2022 Nov 25;13(1):7211. doi: 10.1038/s41467-022-34789-2.

Authors

Daijo Ikuta¹, Eiji Ohtani², Hiroshi Fukui^{3

4}, Takeshi Sakai⁵, Daisuke Ishikawa^{3

4}, Alfred Q R Baron^{6

7}

Affiliations

¹ Department of Earth Science, Tohoku University, Sendai, Miyagi, 980-8578, Japan. dikuta@tohoku.ac.jp.
² Department of Earth Science, Tohoku University, Sendai, Miyagi, 980-8578, Japan. eohtani@tohoku.ac.jp.
³ Materials Dynamics Laboratory, RIKEN SPring-8 Center, Sayo, Hyogo, 679-5148, Japan.
⁴ Japan Synchrotron Radiation Research Institute, Sayo, Hyogo, 679-5198, Japan.
⁵ Geodynamics Research Center, Ehime University, Matsuyama, Ehime, 790-8577, Japan.
⁶ Materials Dynamics Laboratory, RIKEN SPring-8 Center, Sayo, Hyogo, 679-5148, Japan. baron@spring8.or.jp.
⁷ Japan Synchrotron Radiation Research Institute, Sayo, Hyogo, 679-5198, Japan. baron@spring8.or.jp.

Abstract

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.