Crystal structure and hydrogen storage properties of La–Mg–Ni–Co alloy with superstructure

The crystal structure and hydrogen storage properties of the alloys La0.67Mg0.33Ni2.5Co0.5, La0.7Mg0.3Ni2.8Co0.5 and La0.75Mg0.25Ni3.0Co0.5 were investigated. X-ray diffraction results suggested that all the three samples were mainly composed of PuNi3-type, Ce2Ni7-type and Pr5Co19-type phase. These alloys reversibly absorbed and desorbed hydrogen up to ∼1.0 H/M under a hydrogen pressure of 2.5 MPa at 333 K. Moreover, the hexagonal structure of Ce2Ni7-type and Pr5Co19-type was retained during the absorption–desorption process. After hydrogenation, a volumetric expansion of 22.7% was observed for Ce2Ni7-type phase, and an expansion of 1.3% still remained after dehydrogenation.