New crystal structure of Nd2Ni7 formed on the basis of stacking of block layers

Yuki Iwatake, Norihiko L. Okamoto, Kyosuke Kishida, Haruyuki Inui, Jun Ishida, Takuya Kai, Shigekazu Yasuoka

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


The new crystal structure of the intermetallic compound (Nd,Mg)2(Ni,Al)7 has been determined by scanning transmission electron microscopy and electron diffraction. This crystal structure is different from that (either 2H or 3R) usually reported for the intermetallic compound R2T7 (R: rare-earth elements and T: transition-metal elements) in the constitution of block layers. While the block layer for the crystal structure usually reported is of the R2T7 stoichiometric composition consisting of one R2T4 unit layer and two RT5 unit layers, the block layer for the new crystal structure consists of a sub-block layer of the RT3 stoichiometry (formed with one R2T4 unit layer and one RT5 unit layer) and a sub-block layer of the R5T19 stoichiometry (formed with one R2T4 unit layer and three RT5 unit layers), which alternately stack on top of each other. The crystal structure is described based on the order-disorder (OD) theory and the simplest crystal structures (polytypes) among many other polytypes belonging to the same OD family is deduced to be of the 2H-type with the space group of P6¯m2 and of the 6R-type with the space group of R3¯m. The experimentally observed polytype corresponds to the second simplest form of the 6R-type.

Original languageEnglish
Pages (from-to)3023-3034
Number of pages12
JournalInternational Journal of Hydrogen Energy
Issue number7
Publication statusPublished - 2015 Feb 23
Externally publishedYes


  • Hydrogen storage material
  • LaNi
  • Order-disorder (OD) theory
  • Polytype
  • Scanning transmission electron microscopy
  • Superlattice structure

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Fuel Technology
  • Condensed Matter Physics
  • Energy Engineering and Power Technology


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