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

• Published in: Journal of alloys and compounds 2011-08, Vol.509 (32), p.8228-8234
• Main Authors: Li, Daixin, Zhang, Tianran, Yang, Siqi, Tao, Zhanliang, Chen, Jun
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Density; DFT; Electron states; Electronics; Exact sciences and technology; Hydrides; Insulators; Li 2MgH 4; LiMgH 3; Magnesium; Materials science; Mathematical analysis; Methods of electronic structure calculations; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase diagrams of metals and alloys; Physics; Structural prediction; Thermodynamic; Thermodynamic properties
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2011.05.084

► Ground state structures of Li 2MgH 4 and LiMgH 3 are predicted to be Pbam and R 3c. ► The predicted Li-Mg-H compounds are insulators dominated by ionic bonds. ► Preperations of Li-Mg-H compounds through Li, Mg, H 2 are energetically favorable. ► Easily conversion to LiH and MgH 2 limits the stability of the ternary hydrides. 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 LiMgH 3 and Li 2MgH 4 are identified to be R3 c 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 H 2 possess obvious energetic advantage, but may be inhabited kinetically by pure phase separation. Thermodynamically reversible decomposition to LiH and MgH 2 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.