Phase relations and hydrogenation behavior of (La1-xMgx)3Al alloys

The crystal structures and hydrogenation behavior of (La1-xMgx)3Al (x = 0.1, 0.2, 0.3, and 0.4) alloys were investigated. It was found that the alloys with x = 0.1 and 0.2 consist of La(Mg, Al), La, and a novel phase. The novel phase was determined as La2Al. It is shown that the amount of La2Al decreases as the Mg content increases. When x increases to 0.3, only La(Mg,Al) and a small amount of La2Al exist. When x is 0.4, La2Al phase disappears and the alloy contains both La(Mg,Al) and La(Al,Mg)2 Laves phase. The (La0.9Mg0.1)3Al and (La0.7Mg0.3)3Al alloys can be decomposed into LaH3, MgH2, and La2Al5 by the absorption of hydrogen at 473 K.