Unveiling the effect of Ni on the formation and structure of Earth's inner core

TL;DR

This study uses ab initio simulations to show that nickel influences Earth's inner core by affecting phase stability, melting temperatures, and crystallization processes, which could alter our understanding of core formation.

Contribution

It reveals that Ni can stabilize bcc phases, increase melting points, and accelerate Fe crystallization, highlighting its significant role in inner core structure and formation.

Findings

Ni can spontaneously crystallize in liquid at high pressures.

Ni's melting temperature is 700-800 K higher than Fe's at core conditions.

Small amounts of Ni accelerate Fe's crystallization.

Abstract

Ni is the second most abundant element in the Earth's core. Yet, its effects on the inner core's structure and formation process are usually disregarded because of its electronic and size similarity with Fe. Using ab initio molecular dynamics simulations, we find that the bcc phase can spontaneously crystallize in liquid Ni at temperatures above Fe's melting point at inner core pressures. The melting temperature of Ni is shown to be 700-800 K higher than that of Fe at 323-360 GPa. hcp, bcc, and liquid phase relation differ for Fe and Ni. Ni can be a bcc stabilizer for Fe at high temperatures and inner core pressures. A small amount of Ni can accelerate Fe's crystallization at core pressures. These results suggest Ni may substantially impact the structure and formation process of the solid inner core.