Variation of hydrogen occupation in LaNi4.78Sn0.22Dx along the P-C isotherms studied by in situ neutron powder diffraction

We performed in situ neutron powder diffraction measurements of LaN4.78Sn0.22Dx along the absorption and desorption pressure-composition (P-C) isotherms using 90 degrees banks of a TOF diffractometer. Structure of the hydride phase for various hydrogen contents was analyzed by the Rietveld method. Variation of the hydrogen occupation and the lattice parameters for the hydride phase was investigated. The full hydride LaNi4.78Sn0.22D6.1 has a P6mm structure with four hydrogen sites; 3c sites (O[La2Ni4]), 6e(1) sites (T[La2Ni2]), 6e(2) sites (T[La1Ni3]) and 2b sites (T[Ni-4]) with occupancies of 0.98(2), 0.34(1), 0.168(9) and 0.24(2), respectively. The 3c site was fully occupied regardless of the total hydrogen content. Occupancies of the other three sites changed depending on the hydrogen content, with hysteresis between absorption and desorption in the two-phase region. The hydrogen occupation and the lattice parameters for the hydride phase varied even in the two-phase region during desorption. (c) 2006 Elsevier B.V. All rights reserved.