Effect of the partial substitution of Mg by Al on the crystal structure and hydrogenation behavior of La 2Mg 17

Abstract

The effect of the partial substitution of Mg by Al on the crystal structure of La 2Mg 17 has been investigated. It was found that the La 2Mg 17 phase disappears after the partial substitution of Mg by Al. The La 2(Mg 0.9Al 0.1) 17, alloy contains La(Mg, Al) 12 and La(Mg, Al) 2. Further increasing the Al content, the La 2(Mg 0.8Al 0.2) 17 alloy consists of La(Mg, Al) 12, La(Mg, Al) 2, and Mg. The La(Mg 0.93Al 0.07) 12 phase in the La 2(Mg 0.9Al 0.1) 17 alloy crystallizes with the ThMn 12-type structure in space group I4/ mmm (No. 139). The lattice parameters were determined to be a = 1.03246(7) nm and c = 0.59410(6) nm. In the ThMn 12-type structure, Al atoms occupy 8 f site but the Al content is limited. Moreover, the hydrogenation characteristics have also been compared. La 2Mg 17 decomposes into LaH 3 and MgH 2 under hydrogen, but the La(Mg 0.93Al 0.07) 12 phase can be hydrogenated into LaH 3, MgH 2, and La 3Al 11 at 473 K.