Structural disorder, octahedral coordination and two-dimensional ferromagnetism in anhydrous alums

D. V. West, Q. Huang, H. W. Zandbergen, T. M. McQueen, R. J. Cava

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The crystal structures of the triangular lattice, layered anhydrous alums KCr(SO4)2, RbCr(SO4)2 and KAl(SO4)2 are characterized by X-ray and neutron powder diffraction (NPD) at temperatures between 1.4 and 773 K. The compounds all crystallize in the space group P3̄, with octahedral coordination of the trivalent cations. In all cases, small amounts of disorder in the stacking of the triangular layers of corner sharing MO6 octahedra and SO 4 tetrahedra is seen, with the MO6-SO4 network rotated in opposite directions between layers. The electron diffraction study of KCr(SO4)2 supports this model, which on an average can be taken to imply trigonal prismatic coordination for the M3+ ions; as was previously reported for the prototype anhydrous alum, KAl(SO 4)2. The temperature-dependent magnetic susceptibilities for ACr(SO4)2 (A = K, Rb, Cs) indicate the presence of predominantly ferromagnetic interactions. Low-temperature powder neutron diffraction reveals that the magnetic ordering is ferromagnetic in-plane, with antiferromagnetic ordering between planes below 3K.

Original languageEnglish (US)
Pages (from-to)2768-2775
Number of pages8
JournalJournal of Solid State Chemistry
Issue number10
StatePublished - Oct 2008

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry


  • Anhydrous alum
  • Chromium
  • Ferromagnetism
  • Geometric frustration
  • Layered
  • Structural disorder
  • Sulfate
  • Triangular
  • Two-dimensional


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