Crystal structure and electrical characterisation of Bi2NbO5F: an Aurivillius oxide fluoride

Structural characterisation of Bi2NbO5F was performed using X-ray and neutron powder diffraction and electron diffraction. Structural refinements show that the material adopts a distorted structure with significant rotation of the octahedra around two axes. The physical properties of the material have been investigated and show no evidence of polar symmetry. The structure is therefore best described by space group Pbca (a = 5.428(1) angstrom, b = 5.426(1) angstrom, c = 16.656(1) angstrom). Bond valence sum calculations suggest that ordering of the anions in the structure is favourable with the fluorine atoms preferring the apices of the NbX6 (X = O/F) octahedra.