Crystal structures of novel La–Mg–Ni hydrogen absorbing alloys

Crystal structures of La0.70Mg0.30Ni2.5Co0.5 (alloy T1) and La0.75Mg0.25Ni3.0Co0.5 (alloy T2) were investigated. From the structural analysis for small particles picked up from crushed ingot, we found that the alloy T1 consisted of Ce2Ni7-type and PuNi3-type phases and that the alloy T2 consisted of Ce2Ni7-type and Pr5Co19-type phases. These phases were made up two or three blocks that consisted of one [La2Ni4] layer and one to three [LaNi5] layers along c-axis. It was found that Mg occupied the La site in the [La2Ni4] layer. Selective occupation of Mg at the La site in the [La2Ni4] layer makes the alloy stable in repeated hydrogenation and dehydrogenation.