(Nd1.5Mg0.5)Ni7-Based Compounds: Structural and Hydrogen Storage Properties

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• 作者：Qingan Zhang ; Bin Zhao ; Miaohui Fang ; Chaoren Liu ; Qingmiao Hu ; Fang Fang ; Dalin Sun ; Liuzhang Ouyang ; Min Zhu
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：March 5, 2012
• 年：2012
• 卷：51
• 期：5
• 页码：2976-2983
• 全文大小：590K
• 年卷期：v.51,no.5(March 5, 2012)
• ISSN：1520-510X

文摘

The structural and hydrogen storage properties of (Nd_1.5Mg_0.5)Ni₇-based alloys (i.e., A₂B₇-type) with a coexistence of two structures (hexagonal 2H and rhombohedral 3R) are investigated in this study. In both 2H- and 3R-type A₂B₇ structures, Mg atoms occupy Nd sites of Laves-type AB₂ subunits rather than those of AB₅ subunits because Mg substitution for Nd in the AB₂ subunits more significantly strengthens the ionic bond in the system. An increase in the A-atomic radius or the B-atomic radius stabilizes the 2H structure, but a decrease in the A-atomic radius or the B-atomic radius is favorable for formation of the 3R structure. The 2H-A₂B₇ and 3R-A₂B₇ phases in each alloy have quite similar equilibrium pressures upon hydrogen absorption and desorption, which show a linear relationship with the average subunit volume. The hydriding enthalpy for the (Nd_1.5Mg_0.5)Ni₇ compound is about 鈭?9.4 kJ/mol H₂ and becomes more negative with partial substitution of La for Nd and Co/Cu for Ni but less negative with partial substitution of Y for Nd.