Xenon Reacts with Iron at the Conditions of the Earth's Core

TL;DR

This study provides first evidence that xenon can chemically react with iron under Earth's core conditions, forming a stable compound, which suggests the Earth's core could store missing xenon and explains the long-standing Xe paradox.

Contribution

First-principles calculations reveal that xenon reacts with iron at core conditions, forming a stable XeFe3 compound, challenging previous assumptions of inertness.

Findings

Xenon and iron form a stable XeFe3 compound above 183 GPa and 4470 K.

Xenon loses inertness, acting as a 5p-like element in the compound.

The Earth's core can serve as a reservoir for xenon, addressing the missing Xe paradox.

Abstract

Studies of the Earth's atmosphere have shown that more than 90% of xenon (Xe) is depleted compared with its abundance in chondritic meteorites. This long-standing missing Xe paradox has become the subject of considerable interest and several models for a Xe reservoir have been proposed. Whether the missing Xe is hiding in the Earth's core has remained a long unanswered question. The key to address this issue lies in the reactivity of Xe with iron (Fe, the main constituent of the Earth's core), which has been denied by earlier studies. Here we report on the first evidence of the chemical reaction of Xe and Fe at the conditions of the Earth's core, predicted through first-principles calculations and unbiased structure searching techniques. We find that Xe and Fe form a stable, inter-metallic compound of XeFe3, adopting a Cu3Au-type face-centered cubic structure above 183 GPa and at 4470 K. As the result of a Xe -> Fe charge transfer, Xe loses its chemical inertness by opening up the filled 5p electron shell and functioning as a 5p-like element, whilst Fe is unusually negatively charged, acting as an oxidant rather than a reductant as usual. Our work establishes that the Earth's core is a natural reservoir for Xe storage, and possibly provides the key to unlocking the missing Xe paradox.