title: NaCa4Nb5O17: a layered perovskite AnBnO3n+2 compound.
abstract: Sodium tetracalcium pentaniobium heptadecaoxide, NaCa(4)Nb(5)O(17), corresponds to the n = 5 term of the homologous A(n)B(n)O(3n+2) family of structures composed of ABX(3) perovskite layers. The structure consists of perovskite-type blocks of n = 5 layers of NbO(6) octahedra, separated by an interblock region. Successive blocks along the b axis are displaced by 1/2c with respect to each other. The deformation of the NbO(6) octahedra is a minimum at the middle of each block, and increases along the direction of the b axis to a maximum at each end of the block. Ca and Na share the same intrablock sites, coordinated by 12 O atoms, whereas only Ca atoms are found in the interblock cavities, at sites with different coordination geometries.
authors.affiliation: Institut de Cristallographie, Université de Lausanne, BSP Dorigny 1015 Lausanne, Switzerland. wmpzulaj@lg.ehu.es
authors.forename: F J
authors.initials: FJ
authors.lastname: Zúñiga
authors.forename: J
authors.initials: J
authors.lastname: Darriet