| Based on the previous studies of hydrogen storage materials for the La-Mg-Ni ternary alloys, the La-Mg-Co based A5B19-type and the La-Mg-Ni based A2B7-type hydrogen storage alloys are selected as the subjects of this study. (La1-xMgx)5 NiyCo19-y(x=0,0.05,0.10,0.15;y=0,0,0,0,0andx=0,0.02,0.05,0.10,0.15;y=0.5,0.8,1.2, 0.8) and (La1-xMgx)2Ni7.yCoy(x=0,0.02,0.05,0.10,0.15;y=0,0,0,0,0 and x=0,0.05,0.10, 0.15,0.15;y=0.5,0.8,1.2,0.8,1.2) hydrogen storage alloys are weighted, and then melted in the vacuum arc furnace. The crystal structure is examined by X-ray diffractometer. The PowderX software is adopted in processing raw data of XRD patterns. The Pcpdfwin software is applied to research the concrete composition of phase. Then the treated data from the above procedure is indexed by the TREOR and PIRUM programs, which can calculate the values of lattice parameters and volume of every phase. The results show:(La1-xMgx)5 NiyCo19-y hydrogen storage alloys consist of Pr5Co19,LaCo5 and LaSb3V type structures. Furthermore, for (La1-xMgx)5 Co19 alloys, the lattice volume of the main phase structure of Pr5Co19 is decreasing with the increase of Mg content. (Lai_xMgx)2Ni7_yCoy hydrogen storage alloys are composed of LaNis and another type phase structure, that is LaNi3 or La2Ni7 type, except (La0.85Mg0.15)2 Ni7. For (La1-xMgx)2Ni7 alloys, on the contrary, the lattice volume of the main phase structure of LaNis is expanding with the increase of Mg content, which is concluded that doping element Mg replace La and Ni.Then the crystal structure of (Lao.95Mgo.o5)2Ni7 hydrogen storage alloy, which make up of LaNis-type and La2Ni7-type phase structure, is determined by Rietveld method. The weight percentages of the former and latter equal to 25.24wt% and 74.76 wt%, respectively.At last, take La1.60Mg0.36Nd0.83Ni10.18 alloy for example, it is composed of La5Coig,Ce5Ni19 and La2Ni7 phase structure. The lattice parameters of all phases exist a good coherency, which makes for hydrogen storage properties.
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