Phase Transformation and Crystal Structure of La2Ni7Hx Studied by in situ X-ray Diffraction

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• 作者：Kenji Iwase ; Kouji Sakaki ; Yumiko Nakamura ; Etsuo Akiba
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：October 4, 2010
• 年：2010
• 卷：49
• 期：19
• 页码：8763-8768
• 全文大小：826K
• 年卷期：v.49,no.19(October 4, 2010)
• ISSN：1520-510X

文摘

The phase transformation of La₂Ni₇ during hydrogenation was investigated by in situ X-ray diffraction. We found two hydride phases, La₂Ni₇H_7.1 (phase I) and La₂Ni₇H_10.8 (phase II), during the first absorption cycle. The metal sublattice of phase I was orthorhombic (space group Pbcn) with lattice parameters a = 0.50128(6) nm, b = 0.8702(1) nm, and c = 3.0377(1) nm. The sublattice for phase II was monoclinic (space group C2/c) with lattice parameters a = 0.51641(9) nm, b = 0.8960(1) nm, c = 3.1289(1) nm, and β = 90.17(1)°. The lattice parameter c increased with the hydrogen content, while a and b decreased in the formation of phase I from the alloy. Phase transformation from phase I to phase II was accompanied by isotropic expansion. The La₂Ni₄ and LaNi₅ subunit expanded by 48.9% and 6.0% in volume, respectively, during hydrogenation to phase I. They expanded an additional 14% and 5.8%, respectively, in the formation of phase II. The obtained volume expansion suggested different hydrogen distribution in the La₂Ni₄ and LaNi₅ subunit during hydrogenation.