Published online by Cambridge University Press: 21 February 2013
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.