STRUCTURAL-PROPERTIES OF THE COPPER-OXIDE CARBONATE BA4CACU2O6+DELTA-CO3 (DELTA-APPROXIMATE-TO-0)

The structure parameters of Ba4CaCu2O6+deltaCO3 were refined by Rietveld analysis of angle-dispersive neutron powder diffraction data. The stoichiometric metal composition was confirmed by X-ray microanalysis. Iodometry showed that the amount of excess oxygen, delta, was nearly zero. The carbon content and infrared absorption spectrum of the compound gave evidence for the inclusion of CO32- ions in its crystal lattice. Ba4CaCu2O6CO3 is tetragonal with the P4/mmm space group and lattice parameters of a = 5.7879(2) Angstrom and c = 8.1409(3) Angstrom. Ba atoms occupy positions corresponding to the A site in ABO(3) whereas Ca, Cu and C atoms are located at positions corresponding to the B site. Two copper sites are contained in the structure of Ba4CaCu2O6CO3: Cu(1) and Cu(2). If weak bonds between the Cu atoms and O atoms in the CO32- ion are neglected, Cu(1) and Cu(2) are taken as coordinated to four O(1) atoms and two O(2) atoms, respectively. Bond-valence sum calculations showed that the oxidation state of Cu is 2.48 for Cu(1) and 1.66 for Cu(2). The splitting and large thermal parameters of O atoms contained in the CO32- ion revealed its highly disordered orientation.