Superionic Material Might Explain Mysterious Secrets of Earth's Inner Core

The deepest section of the globe, the Earth's core, is characterized by extraordinarily high pressure and temperature. It has a solid inner core and a liquid outer core.

Solidification of Liquid Iron

The solidification of liquid iron at the inner core border causes the inner core to develop and expand. The inner core includes some light elements since it is less dense than pure iron.

The Earth's inner core is formed of a solid iron sublattice and liquid-like light elements, which is also known as a superionic state, according to a collaborative research team led by Prof. HE Yu from the Institute of Geochemistry of the Chinese Academy of Sciences (IGCAS).

Under inner core conditions, the liquid-like light elements are very diffusive in iron sublattices. The research has been published in the Nature magazine (February 9, 2022).

Studying the Planet's Interior

In the interior of planets, a superionic state, a mixture of solid and liquid, is common. Researchers from IGCAS and the Center for High Pressure Science & Technology Advanced Research (HPSTAR) discovered that under inner core conditions, some Fe-H, Fe-C, and Fe-O alloys transformed into a superionic state using high-pressure and high-temperature computational simulations based on quantum mechanics theory.

Light components in superionic iron alloys become disorderly and disperse in the lattice like a liquid. In contrast, iron atoms stay ordered and vibrate around the lattice grid, producing the solid iron framework. In superionic iron alloys, the diffusion coefficients of C, H, and O are the same as in liquid Fe.

"It's a rare occurrence. The mobility of these light elements is not affected by the solidification of iron at the inner core border, and the convection of light elements is constant in the inner core," stated Prof. HE Yu, the study's first and corresponding author, as reported by SciTech Daily.

The inner core's softness and low shear wave velocity have long been a surprise to many people. The researchers noticed a considerable drop in shear wave velocity in these superionic iron alloys when calculating seismic velocities.

"Our findings are in line with the findings of seismologists. The inner core softens because of the liquid-like materials," stated IGCAS co-first author SUN Shichuan.

Factors that Affect Diffusive Light Components

Seismic velocities can be influenced by very diffusive light components, which can help us grasp other mysteries in the deep core.

By addressing the distribution and convection of these liquid-like materials in the inner core, the superionic model may justify the anisotropic structure, seismic wave attenuations, and structural changes of the inner core throughout the last decades.

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