Incommensurately modulated crystal structure of a0 (O03)-type sodium cobalt oxide NaxCoO2 (x ~ 0.78)

Yuzuru Miyazaki, Naoki Igawa, Kunio Yubuta

Research output: Contribution to journalReview articlepeer-review


A single-phase sample of α0 (O03)-type layered sodium cobalt oxide NaxCoO2 (x ~ 0.78) was prepared and its incommensurately modulated crystal structure was analyzed using the (3+1)-dimensional superspace approach to the powder neutron diffraction data. The crystal structure of the cobaltate is accurately described based on the superspace group C2/m(α0γ)00, wherein the positions of Na atoms are most significantly modulated in the monoclinic a direction to form an ordered arrangement. Such a displacive modulation causes a quasi-periodic shift of Na atoms from the centers of the NaO6 polyhedra between undulated CoO2 sheets, changing the form of the NaO6 polyhedron from an octahedral coordination (O) to a trigonal prismatic (P) one, via an intermediate capped trigonal prismatic NaO7 coordination (C). At the positions where the Na atoms are most significantly shifted, the neighboring Na atoms are located at almost touching distances. However, the occupation factor of Na atoms becomes zero at such positions, yielding Na-deficient sites VNa, sandwiched either between C and P, or C and C-type polyhedra.

Original languageEnglish
Pages (from-to)307-308
Number of pages2
JournalActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials
Publication statusPublished - 2021 Jun 1


  • Modulated structure
  • Powder neutron diffraction
  • Rietveld analysis
  • Sodium cobalt oxide
  • Superspace group


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