Synthesis and structure of Ba4CaCu2.24O6.96(CO3)0.5, a perovskite containing carbonate anions, and related phases

Calcination of appropriate mixtures of BaCO3, CaCO3 and CuO has been shown to result in a tetragonal [P4/mmm; a= 5.799(2)Å, c= 7.992(3)Å] perovskite-related phase containing CO32– anions. The unit-cell composition is Ba4CaCu2.24O6.96(CO3)0.5, and powder neutron diffraction has demonstrated that the octahedral sites are occupied by Ca, Cu and C in an ordered fashion. The structure is compared with the cubic phase Ba4CaCu3O8.61. Related phases in which the Ca ions are replaced by other cations are also reported.