SYNTHESIS AND STRUCTURE OF THE TETRAGONAL BA3YCU2OX PHASE - A PEROVSKITE CONTAINING CARBONATE ANIONS

A tetragonal phase has previously been reported in the Ba-Y-Cu-O phase diagram, with approximate Ba:Y:Cu ratio of 3:1:2. Essentially single phase materials with this structure have been synthesised, characterised using thermal analysis, and their structures examined using powder neutron diffraction. The materials are shown to contain CO3(2-) ions, and a typical composition is Ba4YCu2.27(3)O7.08(12)(CO3)0.53(3). The structure (P4/mmm, a = 5.78, c = 8.00 angstrom) is shown to be related to perovskite, and Y, Cu and C atoms are arranged on the octahedral sites in an ordered fashion. The structure is compared with that of a cubic phase, which was reported previously and has a similar cation ratio but no CO3(2-) ions.