Crystal structure and local structure of Mg(2-x)Pr(x)Ni4 (x = 0.6 and 1.0) deuteride using in situ neutron total scattering.

We studied crystal structure and local structure of Mg2–xPrxNi4 (x = 0.6 and 1.0) and their deuterides using in situ neutron total scattering and first-principles calculations. The total scattering data were analyzed using Rietveld refinement and pair distribution function analysis (PDF). The crystal structure of Mg2–xPrxNi4 before deuterium absorption was C15b in space group F43m. No difference between the crystal and local (PDF) structures was observed. The crystal structure of Mg1.0Pr1.0Ni4D∼4 was found to be orthorhombic in space group Pmn21, with three deuterium occupation sites: PrNi3 and two types of bipyramidal Pr2MgNi2 that have a plane of symmetry composed of MgNi2. There is no significant difference between the crystal structure and the local structure of Mg1.0Pr1.0Ni4D∼4. On the other hand, the average crystal structure of the Mg-rich Mg1.4Pr0.6Ni4D∼3.6 was C15b with two deuterium occupation sites: PrNi3 and MgPrNi2 suggesting that the deuterium occupation shifts away from the Pr2MgNi2 bipyra...