Octahedral tilting in the polar hexagonal tungsten bronzes RbNbW2O9 and KNbW2O9

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Abstract

The ambient temperature structures (orthorhombic, space group, Cmc21) of the polar hexagonal tungsten bronzes RbNbW2O9 and KNbW2O9 have been determined by high-resolution powder neutron diffraction. Displacement of the A-site cation in the polar c-axis, with concomitant octahedral tilting, occurs to optimise the A-cation bonding environment reducing the coordination from 18 to 16. This effect is more evident in KNbW2O9 due to decreased A-cation size. The octahedral tilting in both compositions results in a doubling of the c-axis that has not previously been reported, highlighting the importance of neutron diffraction as a complementary technique for structural determination of such systems.
Original languageEnglish
Article numberB75
Number of pages7
JournalActa Crystallographica. Section B, Structural Science
Volume75
Issue numberPart 5
Early online date7 Sept 2019
DOIs
Publication statusPublished - Oct 2019

Keywords

  • Octahedral tilting
  • Polar bears
  • Hexagonal tungsten bronzes
  • Powder neutron diffraction
  • Symmetry mode analysis.

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