Ab initio investigation of structures, electronic and thermodynamic properties for Li–Mg–H ternary system

A systematic consideration of the compounds made up of Li, Mg and H has been taken with respect to the structural, electronic, and thermodynamic properties, by means of density functional theory (DFT). Through the database mining approach, the ground state structures of LiMgH3 and Li2MgH4 are identified to be R3c and Pbam, respectively. The Li–Mg–H ternary hydrides are insulators dominated by ionic bonds besides some covalent components between Mg and H. Energies of different formation pathways have been calculated at finite temperature. Hydrides synthesized from Li, Mg and H2 possess obvious energetic advantage, but may be inhabited kinetically by pure phase separation. Thermodynamically reversible decomposition to LiH and MgH2 brings about another issue for the actual preparation and stable existence of the ternary hydrides. Inserting H atoms to the sites of the ordered alloys with high electric density has been taken as another way to explore possible structures of this system. As H uptakes stepwise, the resulted compounds turn from conductors to insulators. The present results shed light on the design of Li–Mg–H ternary hydrides.

► Ground state structures of Li2MgH4 and LiMgH3 are predicted to be Pbam and R3c.
► The predicted Li-Mg-H compounds are insulators dominated by ionic bonds.
► Preperations of Li-Mg-H compounds through Li, Mg, H2 are energetically favorable.
► Easily conversion to LiH and MgH2 limits the stability of the ternary hydrides.