X-ray diffraction measurements of the Cr-H system were performed by using synchrotron radiation at high H pressures and high temperatures, and the phase diagram was determined at upto p(H2) = 5.5GPa and below 1400K. Three solid phases were found to exist; a body-centered cubic α-phase at low H concentrations ([H]/[Cr] < 0.03) which existed at low H pressures (below 4.4GPa), and 2 high-pressure phases. These were an hexagonal close-packed ε-phase at lower temperatures and a face-centered cubic γ-phase at higher temperatures; both having high H concentrations. A marked reduction in the

melting point was caused by the dissolution of H. A gradual lattice contraction which was observed in the face-centered cubic phase indicated the formation of super-abundant Cr-atom vacancies (vacancy-H clusters). Thermal desorption measurements, performed after recovery from high p(H2) thermal treatments, revealed several desorption stages; including those due to release from vacancy-H clusters and from H-gas bubbles, and permitted the determination of the relevant trapping energies.

Phase Diagram and Superabundant Vacancy Formation in Cr-H Alloys. Y.Fukai, M.Mizutani: Materials Transactions, 2002, 43[5], 1079-84