Detailed measurements of the p (H2)–x –T relation in the face-centered cubic phase of Fe–H alloys revealed the characteristics of supercritical anomalies, with the critical point located at around a H pressure of 4 to 5GPa and 300 to 500C. The vacancy–hydrogen (Vac–H) cluster concentration in the face-centered cubic phase estimated from the lattice contraction was proportional to the H concentration independently of temperature and H pressure. A small lattice contraction due to the superabundant vacancy formation was also observed in the body-centred cubic phase, in accordance with previous thermal desorption measurements, and showed a similar dependence on the H concentration.

The Phase Diagram and Superabundant Vacancy Formation in Fe–H Alloys Revisited. T.Hiroi, Y.Fukai, K.Mori: Journal of Alloys and Compounds, 2005, 404-406, 252-5