A new layered perovskite, KSrNb2O6F, by powder neutron diffraction.

The structure of a new layered oxyfluoride, viz. potassium strontium diniobium hexaoxide fluoride, KSrNb(2)O(6)F, was refined from powder neutron diffraction data in the orthorhombic space group Immm. The oxyfluoride compound is an n = 2 member of the Dion-Jacobson-type family of general formula A[A'(n-1)B(n)X(3n+1)], which consists of double layered perovskite slabs, SrNb(2)O(6)F, between which K(+) ions are located. Within the perovskite slabs, the NbO(5)F octahedra are significantly distorted and tilted about the a axis. A bond-valence-sum calculation gives evidence for O/F ordering in KSrNb(2)O(6)F, with the F(-) ions located in the central sites of the corner-sharing NbO(5)F octahedra along the b axis. All atoms lie on special positions, namely Nb on m, Sr on mmm, K on m2m, F on mm2, and O on sites of symmetry m and m2m.