Uniform patterns of Fe-vacancy ordering in the Kx(Fe,Co) 2- ySe2 superconductors

Sergey M. Kazakov, Artem M. Abakumov, Santiago González, Juan Manuel Perez-Mato, Alexander V. Ovchinnikov, Maria V. Roslova, Alexander I. Boltalin, Igor V. Morozov, Evgeny V. Antipov, Gustaaf Van Tendeloo

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20 Citations (Scopus)


The Fe-vacancy ordering patterns in the superconducting K xFe2-ySe2 and nonsuperconducting K x(Fe,Co)2-ySe2 samples have been investigated by electron diffraction and high angle annular dark field scanning transmission electron microscopy. The Fe-vacancy ordering occurs in the ab plane of the parent ThCr2Si2-type structure, demonstrating two types of patterns. Superstructure I retains the tetragonal symmetry and can be described with the aI = bI = as√5 (as is the unit cell parameter of the parent ThCr2Si2-type structure) supercell and I4/m space group. Superstructure II reduces the symmetry to orthorhombic with the aII = as√2, b II = 2as√2 supercell and the Ibam space group. This type of superstructure is observed for the first time in KxFe 2-ySe2. The Fe-vacancy ordering is inhomogeneous: the disordered areas interleave with the superstructures I and II in the same crystallite. The observed superstructures represent the compositionally dependent uniform ordering patterns of two species (the Fe atoms and vacancies) on a square lattice. More complex uniform ordered configurations, including compositional stripes, can be predicted for different chemical compositions of the KxFe2-ySe2 (0 < y < 0.5) solid solutions.

Original languageEnglish
Pages (from-to)4311-4316
Number of pages6
JournalChemistry of Materials
Issue number19
Publication statusPublished - 11 Oct 2011
Externally publishedYes


  • electron diffraction
  • iron-based superconductors
  • scanning transmission electron microscopy


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