Short-range order stabilizes a cubic iron alloy in Earth's inner core

Area of Science:

• Geophysics
• Materials Science
• Computational Chemistry

Background:

• Earth's inner core composition is primarily iron (Fe) alloyed with light elements, predominantly silicon (Si).
• The precise crystal structure and seismic velocities of Fe-Si alloys under inner core conditions are not well understood.
• Ab-initio methods face challenges predicting properties due to the configurational complexity of these alloys.

Purpose of the Study:

• To determine the Fe-Si binary phase diagram and sound velocities at inner core boundary pressures.
• To identify the most likely crystal structure of Earth's inner core.

Main Methods:

• Integration of a hybrid Monte Carlo sampling algorithm with a deep-learning interatomic potential.
• Computation of the Fe-Si binary phase diagram and sound velocities under high-pressure conditions.

Main Results:

• A complex phase diagram for Fe-Si alloys was computed.
• A body-centered cubic (bcc) phase, stabilized by short-range ordering of Si atoms, was identified.
• The bcc phase accurately reproduces seismic features like low shear-wave velocities and seismic anisotropy.

Conclusions:

• The body-centered cubic (bcc) Fe-Si phase is a leading candidate for Earth's inner core structure.
• Accurate modeling of light-element effects is essential for understanding Earth's core properties.
• This study provides crucial insights into the composition and structure of the deep Earth.