Low reactivity of stoichiometric FeS with hydrogen at high-pressure and high-temperature conditions

Hydrogenation of iron sul fi de (FeS) under high - pressure and high - temperature conditions has attracted attention because hydrogen and sulfur are promising candidates as light elements in the cores of the Earth and other terrestrial planets. In earlier reports describing the hydrogenation of FeS, the chemical compositions of starting materials were not fully clari fi ed. This study reports in - situ neutron and X - ray di ff raction measurements under high - pressure and high - temperature conditions of an Fe - S - H system using a stochiometric Fe 1.000 S (troilite) as a starting material. The site occupancies of hydrogen atoms in FeS, estimated by Rietveld re fi nement of neutron di ff raction patterns collected at about 5 GPa, were 0.014(2) at 700 K and 0.024(2) at 1000 K. The hydrogen occupancy at 900 K and 18.2 GPa was estimated as 0.067(6) from the unit - cell volume determined by X - ray di ff raction using the hydrogen - induced volume expansion calculated from fi rst - principles calculations. These occupancies were signi fi cantly lower than those reported from earlier studies, indicating that the hydrogenation of FeS can be a ff ected strongly by the stoichiometry of iron sul fi de.