Rich magnesium ternary compound so-called LaCuMg₈ derived from La₂Mg₁₇. Structure and hydrogenation behavior

Samuel Couillaud (1) , Etienne Gaudin (1) , Jean-Louis Bobet (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

The magnesium metal rich composition La₁₀TM₁₀Mg₈₀ (with TM = Ni and Cu) were synthesized from the elements in sealed tantalum tubes in an induction furnace. The results show differences depending on the transition metal used. The sample with Ni demixed into ternary and binary compounds with composition close to LaMgNi_2, La₂Mg₁₇ and Mg₂Ni. Only the sample with copper forms a ternary compound. Crystal structure of this new compound was determined by X-ray diffraction on single crystals with an exact formulation La_1.744(5)Cu_1.53(5)Mg_15.73(4). It crystallizes with the La₂Mg₁₇ structure type, space group P6₃/mmc, a = 10.1254(2) Å and c = 10.0751(2) Å. The Mg atoms form hexagonal tubes along the c-axis filled by La and Mg. The Cu atoms are located in these tubes on or around the La and Mg positions, inducing disorder. This compound so-called LaCuMg₈ absorbs around 2 wt% of hydrogen at 603 K, 30 bar and reversibility is possible. Nevertheless, after the first hydrogenation, decomposition into MgH₂, LaH₃ and MgCu₂ have been shown. The pathway of the reaction is described herein.

Domaines: Matériaux

Samuel Couillaud, Etienne Gaudin, Jean-Louis Bobet. Rich magnesium ternary compound so-called LaCuMg₈ derived from La₂Mg₁₇. Structure and hydrogenation behavior. Intermetallics, 2011, 19 (3), pp.336-341. ⟨10.1016/j.intermet.2010.10.011⟩. ⟨hal-00559497⟩