Crystal Structure Evolution of La₂Ni₇ during Hydrogenation

Abstract

Atomic scale characterization of the La2Ni7 hydrides by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that not only the anisotropic expansion of the La2Ni4 unit layer previously reported but also the shearing on the basal plane of the La2Ni4 unit layers occur during one-cycle of hydrogen absorption/desorption process. Two different types of orthorhombic La2Ni7 hydrides with the same atomic arrangement of La and different atomic arrangement of Ni were observed depending on the maximum hydrogen concentration achieved during one hydrogen absorption/desorption cycle.

Thermodynamic and corrosion study of Sm1-Mg Ni (y = 3.5 or 3.8) compounds forming reversible hydrides

“…Consequently, the P-c isotherms of these materials must have a large and flat plateau pressure, lying in the practical electrochemical window (0.001 to 0.1 MPa at room temperature) [1]. In the past twenty years, the ABy compounds with stacking structures (2 < y < 5) [8,9,3,10] have attracted lot of interests due to their high capacity. They can be considered by piling [A2B4] and [AB5] units along the c crystallographic axis.…”