Phase transformation and crystal structure of La2Ni 7Hx studied by in situ X-ray diffraction

Kenji Iwase, Kouji Sakaki, Yumiko Nakamura, Etsuo Akiba

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Abstract

The phase transformation of La2Ni7 during hydrogenation was investigated by in situ X-ray diffraction. We found two hydride phases, La2Ni7H7.1 (phase I) and La2Ni7H10.8 (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.

Original languageEnglish
Pages (from-to)8763-8768
Number of pages6
JournalInorganic Chemistry
Volume49
Issue number19
DOIs
Publication statusPublished - Oct 4 2010

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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