NEUTRON-DIFFRACTION STUDY OF THE DOUBLED PEROVSKITE PHASES BA2M(2-X)CU(X)O(4+DELTA) (M=IN, SC)

Members of the series Ba2M2-xCuxO4-delta (M = In, x = 0.5, 1; M = Sc, x = 1) have been synthesized by solid-state reaction methods and chara cterised by powder neutron diffraction. Selected compositions were ann ealed under oxygen at 1 atm and 160 atm. The evolution of the structur e with oxygen stoichiometry delta was studied. The materials form 'dou bled perovskite' phases, A2BB'O6-x crystallising in tetragonal space g roup P4/mmm. The structures essentially consist of two ABO3-x cubes st acked along the c axis in which the B cations are ordered on two cryst allographically different sites. The divalent Ba cation is on average nine-coordinate and the trivalent M cation octahedrally coordinated to oxygen. The copper oxidation state and coordination varies with the o xygen level of the structure.