Crystal structure analysis of tungsten bronzes β-SrTa 2O 6 and β′-SrTa 2O 6 by synchrotron X-ray and neutron powder diffraction

Eunhye Lee, Cheol Hee Park, Daniel P. Shoemaker, Maxim Avdeev, Young Il Kim

Research output: Contribution to journalArticlepeer-review

Abstract

Strontium ditantalum oxide SrTa 2O 6 exists in α-, β-, and β′-polymorphs. Herein the crystal structures of the latter two were studied using synchrotron X-ray and constant-wavelength neutron powder diffraction. While β′-SrTa 2O 6 [space group P4/mbm, a=12.47099(1) Å, c=3.898210(5) Å, V=606.271(2) Å 3, Z=5] belongs to the regular tetragonal tungsten bronze (TTB) family, it contains locally disordered strontium atoms within the pentagonal channel. β-SrTa 2O 6 [space group Pnam, a=12.36603(2) Å, b=12.43467(2) Å, c=7.72403(1) Å, V=1187.705(4) Å 3, Z=10] can be described as an orthorhombic modification of the TTB, where the octahedral tilting distortion effectively alleviates the bonding strains around TaO 6 and SrO 13 polyhedra. For comparison, rynersonite type α-SrTa 2O 6 [space group Pnma, a=11.00610(6) Å, b=7.63397(3) Å, c=5.62634(3) Å, V=472.727(5) Å 3, and Z=4] is built from edge-shared dimer units of TaO 6 octahedra. As measured by diffuse-reflection absorption spectroscopy, α-, β-, and β′-SrTa 2O 6 have indirect band gap energies of 4.4, 4.0, and 3.8 eV, respectively.

Original languageEnglish (US)
Pages (from-to)232-238
Number of pages7
JournalJournal of Solid State Chemistry
Volume191
DOIs
StatePublished - Jul 2012
Externally publishedYes

Keywords

  • Atomic disorder
  • Bond valence sum
  • Neutron diffraction
  • Tetragonal tungsten bronze

ASJC Scopus subject areas

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

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