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

The crystal structure and hydrogenation properties of Gd 2 Co 7 -type Y 2 Ni 7 were investigated by X-ray diffraction (XRD), Sievert’s method, and neutron powder diffraction. Unlike Nd 2 Ni 7 and La 2 Ni 7, Y 2 Ni 7 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 A 2 B 7 D x 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.