CRYSTAL-STRUCTURE OF BIPBSR2MNO6 BY POWDER NEUTRON-DIFFRACTION

The structure and the oxygen stoichiometry of the layered oxide BiPbSr 2MnO6 has been examined by profile analysis from powder neutron diffra ction data. The structure was refined in the space group Amaa (n degre es 66). The material has orthorhombic symmetry with lattice parameters a=5.3204(3), b=5.3796(3) and c=23.714(1)Angstrom. Its structure is an alogue to that of superconducting cuprate Bi2Sr2CuO6+delta, but withou t modulation. An important structural feature of BiPbSr2MnO6 is that t he oxygens in the (Bi,Pb)O layer are disordered over two positions alo ng the a-axis. The calculated effective valence of manganese is 3.2. T he MnO6 octahedra are elongated along the c-axis, characteristic of th e Jahn-Teller distortion of octahedra with Mn3+ ions.