Jahn-Teller ordering in Kagomé-type layers of compounds A2A′MnIII3F12 (A = Rb, Cs; A′ = Li, Na, K)

Ulrich Englich, Christoph Frommen, Werner Massa

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

For a series of new Mn(III) fluorides the crystal structures have been determined by X-ray diffraction on single crystals: Cs2LiMn3F12, space group R3̄, Z = 3 (merohedral twin), a = 7.440(1), c = 17.267(3) Å, R = 1.95%; three isostructural triclinic phases, space group P1̄, Z = 2, Cs2NaMn3F12, a = 7.305(1), b = 7.512(1), c = 10.376(2) Å, α = 89.89(3)°, β = 87.32(3)°, γ = 89.89(3)°, R = 2.75%; Rb2NaMn3F12, a = 7.115(1), b = 7.482(1), c = 10.160(2) Å, α = 89.92(3)°, β = 86.52(3)°, γ = 89.51(3)°, R = 2.70%; Rb2LiMn3F12, a = 6.883(1), b = 7.481(1), c = 10.194(2) Å, α = 89.42(3)°, β = 87.16(3)°, γ = 90.25(3)°. R = 4.87%; monoclinic Cs2KMn3F12, space group C2/c, Z = 4, a = 13.112(3), b = 7.571(2), c = 12.672(3) Å, β = 108.79(3)°, R = 5.3%. All structures derive from the Cs2NaAl3F12 parent structure and consist of [Mn3F12] layers of corner-sharing octahedra of the Kagomé-net-type (3+6 octahedra units like in the hexagonal tungsten bronze layers). The [MnF6] octahedra are strongly elongated by the Jahn-Teller effect with ratios of long to short axes of about 1.15. In all structures the long axes are oriented within the layers in an alternating wind-wheel-like pattern corresponding to an antiferrodistortive Jahn-Teller ordering. Thus, all Mn-F-Mn bridges are asymmetric; the bridge angles are between 136° and 141°. Magnetic investigations of Cs2NaMn3F12 and Cs2KMn3F12 indicate similar antiferromagnetic exchange interactions (J/k = -2.5 K), but only for the Cs2K compound has 2D and 3D ordering been found at low temperatures. The results are discussed in context with the Jahn-Teller ordering and the 'frustrated' exchange situation in the Kagomé net.

Original languageEnglish (US)
Pages (from-to)155-165
Number of pages11
JournalJournal of Alloys and Compounds
Volume246
Issue number1-2
DOIs
StatePublished - Jan 15 1997
Externally publishedYes

Keywords

  • Crystal structures
  • Fluoromanganates(III)
  • Jahn-Teller ordering
  • Magnetism
  • Manganese(III)

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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