The structure and phase diagram of M-H systems at high chemical potentials-High pressure and electrochemical synthesis

Efforts to provide a unified picture of metal-hydrogen alloys over a wide range of chemical potentials are described. High chemical potentials are produced either by high-pressure molecular hydrogen or high excess potentials in electrolytic charging or electrodeposition. General systematics of the phase diagram of 3d-metal-hydrogen systems are noted; a drastic reduction of the melting point and the stabilization of close-packed structures with dissolution of hydrogen. Supercritical anomalies are observed in the fcc phase of Fe-H, Co-H and Ni-H systems. In the electrodeposition of metals, it is shown that structural changes are caused by dissolution of hydrogen, and superabundant vacancies of concentrations ∼ 10−4 are present.