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Title: Evidence of Intermediate Hydrogen States in the Formation of a Complex Hydride

A complex hydride (LaMg 2NiH 7) composed of La 3+, two Mg 2+, [NiH 4] 4– with a covalently bonded hydrogen, and three H was formed from an intermetallic LaMg 2Ni via an intermediate phase (LaMg 2NiH 4.6) composed of La, Mg, NiH 2, NiH 3 units, and H atoms at tetrahedral sites. The NiH 2 and NiH 3 units in LaMg 2NiH 4.6 were reported as precursors for [NiH 4] 4– in LaMg 2NiH 7 [Miwa et al. J. Phys. Chem. C 2016, 120, 5926–5931]. To further understand the hydrogen states in the precursors (the NiH 2 and NiH 3 units) and H atoms at the tetrahedral sites in the intermediate phase, LaMg 2NiH 4.6, we observed the hydrogen vibrations in LaMg 2NiH 4.6 and LaMg 2NiH 7 by using inelastic neutron scattering. A comparison of the hydrogen vibrations of the NiH 2 and NiH 3 units with that of [NiH 4] 4– shows that the librational modes of the NiH 2 and NiH 3 units were nonexistent; librational modes are characteristic modes for complex anions, such as [NiH 4] 4–. Furthermore, the hydrogen vibrations for the H atoms in the tetrahedral sites showed a narrower wavenumber rangemore » than that for H and a wider range than that for typical interstitial hydrogen. The results indicated the presence of intermediate hydrogen states before the formation of [NiH 4] 4– and H .« less
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [3] ;  [4]
  1. Tohoku Univ., Sendai (Japan). Inst. for Materials Research
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division, Neutron Sciences Directorate
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division, Neutron Sciences Directorate
  4. Tohoku Univ., Sendai (Japan). Inst. for Materials Research; Tohoku Univ., Sendai (Japan). WPI-Advanced Inst. for Materials Research
Publication Date:
Grant/Contract Number:
AC05-00OR22725; 16K06766; 25220911
Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Volume: 57; Journal Issue: 2; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Laboratory Directed Research and Development (LDRD) Program; Japan Society for the Promotion of Science (JSPS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Inelastic neutron scattering; complex hydride; hydrogen state
OSTI Identifier:
1422532