Structural and Hydrogen Storage Properties of Y₂Ni₇ Deuterides Studied by Neutron Powder Diffraction

The crystal structure and hydrogenation properties of Gd2Co7-type Y2Ni7 were investigated by X-ray diffraction (XRD), Sievert’s method, and neutron powder diffraction. Unlike Nd2Ni7 and La2Ni7, Y2Ni7 exhibits three plateau pressures and forms three hydrides at room temperature. The maximum hydrogen capacity reaches 8.9 H/fu at 10 MPa at the first absorption cycle. The compound can be cycled by a solid–gas route, and structural properties are fully recovered after dehydrogenation. For the first time, the structural properties of rhombohedral A2B7Dx deuterides were studied. They were investigated by neutron powder diffraction at three different states of charge (x = 2.1, 4.1, and 8.8). Deuterium positions as well as variation of unit cell parameters are given and discussed in this paper.