Transition metal-based hydrides: combining in-situ and high-resolution neutron powder diffraction studies

In this study we focused on those metal hydrides, which could be traditionally considered as “interstitial”, but their structures appear to be highly influenced by transition metal-hydrogen (T-H) interaction. Each metal-hydrogen system has been studied first by in-situ NPD (DMC) under controlled deuterium pressure, and then the individual phases were studied ex-situ by high resolution NPD (HRPT). Each system revealed two to three hydride phases, stable at certain temperatures and pressures (deuterium concentrations). While the symmetry of a deuteride structure is usually lower than that of the corresponding alloy, a metal atom substructure may undergo a complete reconstruction upon hydrogenation. In some systems the T-H contacts appear to be short and directed (like in non-metallic complex transition metal hydrides), thus affecting a structure and properties of the hydride phases. In my talk these observations will be illustrated with the following systems: • HoNi3-D2 [1]: three hydride phases; R-3m → R3m transition; ordered pyramidal [NiD3] fragments; • ErCo3-D2 [2]: two hydride phases; symmetry preserved; disordered octahedra