In situ X-ray diffraction measurements at high temperatures and high H pressures were performed on Fe–H alloys and, together with available data, yielded a p(H2)–T diagram for up to 10GPa and 1500C. A marked reduction in the melting point, with dissolution of H, down to 800C at 3GPa, was observed. In the face-centered cubic phase, a gradual lattice contraction due to super-abundant vacancy formation was found to take place over several hours. The lattice parameter at 784C, 4.7GPa decreased by 6%, which implied that a vacancy concentration as high as 19at% was attained.

The Phase Diagram and Superabundant Vacancy Formation in Fe–H Alloys under High Hydrogen Pressures. Y.Fukai, K.Mori, H.Shinomiya: Journal of Alloys and Compounds, 2003, 348[1-2], 105-9