Thermally robust anion-chain order in oxynitride perovskites

Lucy Clark, Judith Oró-Solé, Kevin S. Knight, Amparo Fuertes*, J. Paul Attfield

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The presence and thermal stability of anion order in the oxynitride perovskites SrTaO2N and LaTaON2 have been determined using high resolution powder neutron and electron diffraction data. Partial order of oxide and nitride anions consistent with the formation of planes of disordered cis-anion chains is observed in both materials, with a chemical symmetry between distributions in SrTaO2N and LaTaON2. No loss of anion order is observed up to 1100 C and extrapolations based on lattice strains show the order to be stable to remarkably high temperatures >2000 C, demonstrating that anions are segregated when the materials are synthesized. SrTaO 2N has an apparent tetragonal I4/mcm superstructure at room temperature due to ordered octahedral tilts, but anion order lowers symmetry to an orthorhombic Fmmm supercell (with lattice parameters a = 8.0657(8), b = 8.0614(7), and c = 8.0775(4) Å). Anion order also lowers the symmetry of LaTaON2 from apparent orthorhombic Imma to monoclinic I2/m (a = 5.7140(6), b = 8.0595(6), c = 5.7506(5) Å, and β = 90.239(4) at 20 C) and this superstructure persists up to 1100 C with an extrapolated loss of tilting at 1540 C. Anion order appears to direct octahedral tilting such that the more rigid Ta-N-Ta bridges retain bond angles closer to 180 than the Ta-O-Ta connections in these superstructures.

Original languageEnglish
Pages (from-to)5004-5011
Number of pages8
JournalChemistry of Materials
Volume25
Issue number24
Early online date9 Dec 2013
DOIs
Publication statusPublished - 23 Dec 2013

Keywords

  • anion order
  • oxynitrides
  • perovskites
  • powder neutron diffraction

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