Iron Hydride in the Earth's Inner Core

Abstract

Hydrogen is potentially a key light element in the Earth’s core. Determining the stability of iron hydride is essential for Earth's core mineralogy applications. We investigated the thermal stabilities and seismic properties of a range of Fe-H binary at core P-T conditions. It is concluded that H induces a phase change in the Fe lattice, converting it from hcp to fcc. With 1 wt.% H incorporation, the density of Fe decreases by 7.6%, both the compressional and shear wave velocities increase by 2.3% and 1.5%, respectively. The maximum H concentration is estimated to be ~0.57 wt.% to explain the density deficit of the inner core, which corresponds to 3 times as much as seawater, indicating that a large amount of water has been brought to the Earth's interior during its formation and a relatively low inner core temperature thus induced. H alongside other light elements are required to account for the geophysical observations of the Earth's inner core.