title: Cation deficient layered Ruddlesden-Popper-related oxysulfides La2LnMS2O5 (Ln=La, Y; M=Nb, Ta).
abstract: The structures of the new oxysulfide Ruddlesden-Popper phases La2LnMS2O5 (Ln=La, Y; M=Nb, Ta) are reported together with an iodide-containing variant: La3-xNb1+xS2O5I2x (0<or=x<0.11). Structures were refined against powder-neutron or single-crystal X-ray diffraction data. All of these compounds exhibit an intergrowth structure with NaCl-type slabs [La2S2] alternating regularly with perovskite-type oxide slabs [LnMO5] or [La1-xNb1+xO5I2x]. In the oxide slabs, the trivalent and pentavalent cations are disordered on the long-length scale probed by diffraction methods, but bond length considerations suggest that they must be ordered at least on the length scale of the unit cell. The [LnMO5] block of the iodide-free compounds derive from the ideal [Ti2O5] blocks found in Ln2Ti2S2O5 (Ln=Nd-Er; Y) by the formal substitution of two Ti4+ ions with one Ln3+ and one M5+ion. The unusual partial insertion of iodide in the perovskite voids of the [LaNbO5] block in La3NbS2O5 was found to be coupled to a La/Nb substitution, maintaining the charge balance within the [La1-xNb1+xO5I2x]2- block. The Nb5+ ions were found to be too resistant to reduction to undergo the intercalation of alkali metals observed in the Ln2Ti2S2O5 series.
authors.affiliation: Institut des Matériaux Jean Rouxel, Laboratoire de Chimie des Solides, 2, rue de la Houssinière, BP 32229, 44322 Nantes cedex 3 - France. laurent.cario@cnrs-imn.fr
authors.forename: Laurent
authors.initials: L
authors.lastname: Cario
authors.forename: Aurelian Florin
authors.initials: AF
authors.lastname: Popa
authors.forename: Alain
authors.initials: A
authors.lastname: Lafond
authors.forename: Catherine
authors.initials: C
authors.lastname: Guillot-Deudon
authors.forename: Houria
authors.initials: H
authors.lastname: Kabbour
authors.forename: A
authors.initials: A
authors.lastname: Meerschaut
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Clarke
authors.forename: Paul
authors.initials: P
authors.lastname: Adamson