La7Ru3O18 and La4.87Ru2O12: Geometric frustration in two closely related structures with isolated RuO6 octahedra

P. Khalifah, Q. Huang, D. M. Ho, H. W. Zandbergen, R. J. Cava

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The crystal structures of La7Ru3O18 and La4.87Ru2O12 have been solved from powder neutron diffraction data (R(p) = 0.032) and single-crystal X-ray diffraction data (R(w) = 0.070 for all 3125 reflections), respectively. Although these compounds are both the first example of their structure types, La7Ru3O18, La4.87Ru2O12, and the known compound Sr5Re2O12 all have closely related structures. La7Ru3O18 crystallizes in the rhombohedral space group R3c, with cell constants of a = 9.83677(23) Å and c = 56.3493(16) Å in the hexagonal setting, and with Z = 12 formula units per cell. Monoclinic La4.87Ru2O12 crystallizes in the P21/c space group with cell constants of a = 5.5798(6) Å, b = 10.1286(11) Å, c = 19.0095(20) Å, β = 90.815(4)°, and Z = 4. These structures contain isolated RuO6 octahedra (d(Ru-Ru)~5.7 Å), which are organized into well-defined layers having trigonal or pseudo-trigonal symmetry. Furthermore, the three-dimensional patterning of Ru atoms is a nearly perfect close-packed arrangement, despite the large Ru-Ru distances. Magnetic measurements show that geometric frustration suppresses the ordering of the Ru spins and that monoclinic La4.87Ru2O12 is more frustrated than rhombohedral La7Ru3O18. (C) 2000 Academic Press.

Original languageEnglish (US)
Pages (from-to)189-197
Number of pages9
JournalJournal of Solid State Chemistry
Issue number1
StatePublished - 2000

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


  • Antiferromagnets
  • Geometric frustration
  • LaRuO
  • LaRuO; SrReO
  • Lanthanum ruthenium oxides
  • Valence bond sum


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