Effect of the partial substitution of Mg by Al on the crystal structure and hydrogenation behavior of La2Mg17

The effect of the partial substitution of Mg by Al on the crystal structure of La2Mg17 has been investigated. It was found that the La2Mg17 phase disappears after the partial substitution of Mg by Al. The La2(Mg0.9Al0.1)17, alloy contains La(Mg, Al)12 and La(Mg, Al)2. Further increasing the Al content, the La2(Mg0.8Al0.2)17 alloy consists of La(Mg, Al)12, La(Mg, Al)2, and Mg. The La(Mg0.93Al0.07)12 phase in the La2(Mg0.9Al0.1)17 alloy crystallizes with the ThMn12-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 ThMn12-type structure, Al atoms occupy 8f site but the Al content is limited. Moreover, the hydrogenation characteristics have also been compared. La2Mg17 decomposes into LaH3 and MgH2 under hydrogen, but the La(Mg0.93Al0.07)12 phase can be hydrogenated into LaH3, MgH2, and La3Al11 at 473 K.