Octahedral tilting in the polar hexagonal tungsten bronzes RbNbW2O9 and KNbW2O9
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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.
McNulty , J A , Gibbs , A , Lightfoot , P & Morrison , F D 2019 , ' Octahedral tilting in the polar hexagonal tungsten bronzes RbNbW 2 O 9 and KNbW 2 O 9 ' , Acta Crystallographica. Section B, Structural Science , vol. 75 , no. Part 5 , B75 . https://doi.org/10.1107/S2052520619009260
Acta Crystallographica. Section B, Structural Science
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DescriptionWe thank the Science and Technology Facilities Council (STFC) for the provision of neutron diffraction facilities at ISIS (HRPD experiment RB1710021, doi: 10.5286/ISIS.E.RB1710021) and the School of Chemistry, University of St Andrews for funding of a studentship to JAM through the EPSRC doctoral training grant (EP/K503162/1).
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