Helium-iron compounds at terapascal pressures

TL;DR

This study uses first-principles calculations to reveal stable helium-iron compounds at terapascal pressures, predicting new phases and melting behaviors relevant to planetary and stellar interiors.

Contribution

It is the first to identify stable helium-iron compounds and their phase diagram at ultrahigh pressures using computational methods.

Findings

FeHe stable above 4 TPa

FeHe$_2$ stable above 12 TPa

Predicted superionic phase with helium sublattice melting

Abstract

We investigate the binary phase diagram of helium and iron using first-principles calculations. We find that helium, which is a noble gas and inert at ambient conditions, forms stable crystalline compounds with iron at terapascal pressures. A FeHe compound becomes stable above 4 TPa, and a FeHe$_2$ compound above 12 TPa. Melting is investigated using molecular dynamics simulations, and a superionic phase with sublattice melting of the helium atoms is predicted. We discuss the implications of our predicted helium-iron phase diagram for interiors of giant (exo)planets and white dwarf stars.