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Octahedral tilting in the polar hexagonal tungsten bronzes RbNbW 2 O 9 and KNbW 2 O 9
Author(s) -
McNulty Jason A.,
Gibbs Alexandra S.,
Lightfoot Philip,
Morrison Finlay D.
Publication year - 2019
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520619009260
Subject(s) - orthorhombic crystal system , octahedron , crystallography , neutron diffraction , tungsten , polar , materials science , crystal structure , diffraction , chemistry , physics , optics , metallurgy , astronomy
The ambient‐temperature structures (orthorhombic, space group Cmc 2 1 ) of the polar hexagonal tungsten bronzes RbNbW 2 O 9 and KNbW 2 O 9 have been determined by high‐resolution powder neutron diffraction. Displacement of the A ‐site cation along the polar c axis with concomitant octahedral tilting occurs to optimize the A cation bonding environment, hence reducing the coordination from 18 to 16. This effect is more evident in KNbW 2 O 9 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.