Hydrogenation and structural properties of Mg100-2xLixAlx (x=12) limited solid solution.

Abstract Mg-rich region of phase diagram of the Mg-Li-Al ternary system was investigated by means XRD, SEM/WDS and EPMA methods. The Mg-based solid solution extend up to Mg 76 Li 12 Al 12 composition. The Mg 76 Li 12 Al 12 H x hydrides were prepared by different methods, such as gas phase hydrogenation and thermal synthesis. Two hydride phases forms at the interaction of Mg 76 Li 12 Al 12 alloy with hydrogen. In the first stage, the insertion of hydrogen in to the structure of the initial hexagonal phase up to the maximum content of hydrogen equal 3.2 wt.% was observed. This Mg 76 Li 12 Al 12 H x (0 < x < 74) reversible hydride has a hexagonal crystal structure (P-6m2 , a  = 3.1485(1), c  = 5.1111(2) Å) in which the hydrogen atoms inserts to octahedral voids. During the next stage of hydrogenation a new Mg 76 Al 12 Li 12 H x (74 < x < 200) hydride phase with higher hydrogen content up to 8.2 wt.% H 2 is formed. This hydride has a orthorhombic structure (Cmmm , a  = 6.8198(3), b  = 6.8543(3), c  = 3.3609(1) Å) in which the hydrogen atoms has coplanar triangle coordination. This orthorhombic hydride has also higher hydrogen content in compare to binary MgH 2 hydride (7.6 wt.% H 2). Graphical abstract Image Highlights • Synthesis of alloys. • Phase diagram. • Intermetallic. • Hydrides. • Crystal structure investigations. [ABSTRACT FROM AUTHOR]