X-ray diffraction and Mössbauer spectroscopy study of fcc iron hydride FeH at high pressures and implications for the composition of the Earth's core

The phase fcc FeHx (x ~ 1) was synthesized at pressures over 30 GPa and temperatures over 1600(50) K. At room temperature this iron hydride is stable at pressures from 19(1) GPa up to at least 68(2) GPa (the highest pressure achieved in this study). A fit of the PV data collected for fcc FeHx at room temperature gives the following parameters for the equation of state: V0 = 53.8(3) Å3, K0 = 99(5) GPa, K′ = 11.7(5). Using this data the amount of H required to match the density of the Earth's core was estimated to be 0.5–1 wt.% hydrogen in the outer core and 0.08–0.16 wt.% hydrogen in the inner core. Our results also suggest that hydrogen and carbon do not occur together in the Earth's core.

Research highlights► The synthesis of the fcc FeHx (x ~ 1) is monitored by in-situ X-ray diffraction spectroscopy. ► The room temperature equation of state of the fcc FeHx is measured up to 68 GPa. ► The possible hydrogen budget in the Earth's core is estimated. ► The presence of both hydrogen and carbon in the Earth's core s unlikely.