This work focused on the high pressure PCT and
in situ neutron powder diffraction studies of the LaMg
2Ni
9-H
2 (D
2) system at pressures up to 1,000 bar. LaMg
2Ni
9 alloy was prepared by a powder
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This work focused on the high pressure PCT and
in situ neutron powder diffraction studies of the LaMg
2Ni
9-H
2 (D
2) system at pressures up to 1,000 bar. LaMg
2Ni
9 alloy was prepared by a powder metallurgy route from the LaNi
9 alloy precursor and Mg powder. Two La
3−xMg
xNi
9 samples with slightly different La/Mg ratios were studied, La
1.1Mg
1.9Ni
9 (sample 1) and La
0.9Mg
2.1Ni
9 (sample 2).
In situ neutron powder diffraction studies of the La
1.09Mg
1.91Ni
9D
9.5 (1) and La
0.91Mg
2.09Ni
9D
9.4 (2) deuterides were performed at 25 bar D
2 (1) and 918 bar D
2 (2). The hydrogenation properties of the (1) and (2) are dramatically different from those for LaNi
3. The Mg-containing intermetallics reversibly form hydrides with DH
des = 24.0 kJ/mol
H2 and an equilibrium pressure of H
2 desorption of 18 bar at 20 °C (La
1.09Mg
1.91Ni
9). A pronounced hysteresis of H
2 absorption and desorption, ~100 bar, is observed. The studies showed that LaNi
5-assisted hydrogenation of MgNi
2 in the LaMg
2Ni
9 hybrid structure takes place. In the La
1.09Mg
1.91Ni
9D
9.5 (1) and La
0.91Mg
2.09Ni
9D
9.4 (2) (a = 5.263/5.212; c = 25.803/25.71 Å) D atoms are accommodated in both Laves and CaCu
5-type slabs. In the LaNi
5 CaCu
5-type layer, D atoms fill three types of interstices; a deformed octahedron [La
2Ni
4], and [La(Mg)
2Ni
2] and [Ni
4] tetrahedra. The overall chemical compositions can be presented as LaNi
5H
5.6/5.0 + 2*MgNi
2H
1.95/2.2 showing that the hydrogenation of the MgNi
2 slab proceeds at mild H
2/D
2 pressure of just 20 bar. A partial filling by D of the four types of the tetrahedral interstices in the MgNi
2 slab takes place, including [MgNi
3] and [Mg
2Ni
2] tetrahedra.
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