In-situ powder neutron diffraction study on the formation process of LaMg2NiH7

Abstract The formation process from the intermetallic compound LaMg 2 Ni to a complex hydride (deuteride) LaMg 2 NiD 7 composed of La 3+ , 2 × Mg 2+ , [NiD 4 ] 4− , and 3 × D − was investigated by in-situ powder neutron diffraction under deuterium gas pressure at room temperature. Below 0.001 MPa, small amount of deuterium was initially dissolved in the lattice of LaMg 2 Ni forming LaMg 2 NiD 0.05 and two new hydride phases (LaMg 2 NiD x 1 and LaMg 2 NiD x 2 ) were continuously yielded. Furthermore, LaMg 2 NiD 4.6 with NiD 1.9 and NiD 3.3 units and interstitial deuterium atoms was formed prior to appearing of LaMg 2 NiD 7 . From their Bragg peak positions, the deuterium contents x 1, and x 2 were inferred as 0.05  x 1  x 2  2 NiD 7 started forming. Since the intermediate deuterides had similar metal atomic framework of LaMg 2 Ni, we revealed that LaMg 2 NiD 7 formation proceeded through multiple deuteride phases with maintaining of the metal atomic framework of LaMg 2 Ni.