ABSTRACTAtomic 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.