The effect of the rare earth elements and alloy composition on the hydrogenation properties and crystal structures of hydrides in Mg 2-xRE xNi 4 (RE = La, Pr, Nd, Sm, and Gd; x = 0.6 and 1.0) was investigated. All Mg 2-xRE xNi 4 alloys had a C15b Laves phase before hydrogenation. Mg 1.4RE 0.6Ni 4 (RE = Pr, Sm, and Gd) alloys were hydrogenated through one plateau to form Mg 1.4RE 0.6Ni 4H ∼3.6 while maintaining the C15b structure. Mg 1.0RE 1.0Ni 4 (RE = La, Pr, and Nd) alloys were hydrogenated to ∼1.0 H/M proceeding through two plateaus, and Mg 1.0RE 1.0Ni 4 (RE = Sm and Gd) alloys were hydrogenated to 0.6-0.7 H/M through one plateau. Mg 1.0RE 1.0Ni 4 alloys initially transformed into Mg 1.0RE 1.0Ni 4H ∼4 with an orthorhombic structure. In addition it was experimentally confirmed that Mg 1.0RE 1.0Ni 4H ∼4 with La, Pr, and Nd transformed into Mg 1.0RE 1.0Ni 4H ∼6 with a C15b structure, while no formation of Mg 1.0RE 1.0Ni 4H ∼6 (RE = Sm and Gd) was observed at 40 MPa at 250 K. Theoretical calculations suggest that Mg 1.0RE 1.0Ni 4H ∼4 with Sm and Gd also transform to Mg 1.0RE 1.0Ni 4H ∼6 at higher pressures than those used in our experiments (264 MPa for Mg 1.0Sm 1.0Ni 4 and 8.5 GPa for Mg 1.0Gd 1.0Ni 4 at 253 K). It was found that the hydrogenation properties and crystal structure of the hydrides in Mg 2-xRE xNi 4 are dependent on the alloy composition, i.e., the ratio of Mg to RE in the alloy phase, but independent of the choice of rare earth element.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films