Neutron diffraction of samarium deuteride.

Abstract

Studies are being performed on the crystal structure of rare earth metal hydrides for use as hydrogen storage systems. As hydrogen is added to the metal, a face centered cubic hydride is farmed. Additional hydrogen is then absorbed and the metal lattice reduces its size. In the lighter rare earths, this reduction in lattice size appears to a stoichiometry of MH3•0, With samarium and the heavier rare earths. the face centered cubic absorbs hydrogen and then undergoes a solid phase transition to a hexagonal structure capable of absorbing hydrogen up to the MH3•0 limit. The location of the hydrogen atoms within the cubic and hexagonal phases around the transition is the focus of this project. These atom positions can best be detected by neutron diffraction techniques applied to different stoichiometries, both cubic and hexagonal. bracketing the transition. The experiments were performed on samarium-154 deuteride. My part in this ongoing research involve first designing and building a system of known volume. Then, different stoichiometric samples of samarium deuteride. using determined P-T-C conditions. were prepared. A neutron diffraction pattern was run on each sample. Interpretation of this pattern provided an analysis of the hydrogen locations in the cubic and hexagonal crystal lattices.