Synthesis, crystal structure and magnetic properties of Ba5Ru2O9(O2), Ba5Nb2O9(O2) and Ba5Ru2O10 related to the perovskite-type structure, and structural relationships with corresponding sulfides

The compound Ba5Nb2O9(O-2) has been synthesized by solid state reactions. The crystal structure has been refined from X-ray powder data. Ba5Nb2O9(O-2) is isostructural with Ba5Ru2O9(O-2) with the cell parameters a = 6.045(1)Angstrom, c = 18.316(3)Angstrom (P6(3)/mmc). Perpendicular to the c-axis, the structure is built up by the periodic stacking of three close packed [BaO3] layers separated by a layer of composition [Ba2O2] containing (O-2)(2-) peroxide ions. The compound Ba5Ru2O10 has been obtained by thermal decomposition of Ba5Ru2O9(O-2). The structure has been refined from X-ray powder data. The structure is similar to Ba5Ru2O9(O-2) but now the composition of the layer is [Ba2O]. The magnetic properties of Ba5Ru2O9(O-2) and Ba5Ru2O10 have been interpreted in terms of isolated dimers and confirm the structural results. All these phases belong to a new family of compounds formulated as [A(2)(O-2)][A(n)B(n - 1)O(3n)] where n represents the number of [AO(3)] successive layers in the hexagonal perovskite slabs. This series is extended to ternary barium sulfides. (C) 1999 Elsevier Science S.A. All rights reserved.