STRUCTURE OF THE YBA4CU2(CO3)O-5.5+ -DELTA OXYCARBONATE/

The crystal structure of the YBa4Cu2(CO3)O-5.5+/-delta ((142') oxycarb onate has been investigated by X-ray and neutron powder diffraction te chniques, X-ray diffraction patterns indexed as a tetragonal P4/m unit cell with lattice parameters a = 8.1973 (4) and c = 8.0360(5) Angstro m. Rietveld refinements of powder neutron diffraction data indicated a distorted cubic perovskite cell in which yttrium and copper are arran ged to yield a superlattice double that of the typical perovskite unit . Refinements indicate CO32- ions substituted on two of the four Cu si tes in the proposed cell. Infrared spectroscopy results were consisten t with neutron structural analysis, giving strong supporting evidence to the presence of two unique carbonate sites in the unit cell.