The structures of Pb2Sr2YCu3O8+δ with δ=1.46, 1.61, 1.71, have been determined by powder neutron diffraction data. As previously shown for Pb2Sr2YCu3O9.32, the extra oxygen atoms are incorporated on the Cu layer sandwiched between two PbO layers. The structural refinements indicated that the most stable structure is that of Pb2Sr2YCu3O9.5 in which the two possible oxygen sites on the Cu layer are filled up to 75%. These extra oxygen atoms give rise to superstructures and change the coordination of the cations belonging to the (PbO)(Cu)(PbO) blocks. In Pb2Sr2YCu3O9.5 the Cu cations inside these blocks are surrounded by an oxygen pyramid, while the Pb cations are surrounded by seven, eight, or nine oxygen atoms, depending upon the specific site in the superstructure. At the same time, the valences of these cations increase from 1+ to 2+ for Cu and from 2+ to 4+ for half of the Pb. The oxidation of the Pb cations hinders the charge transfer from the CuO1.5 layers to the superconducting (CuO2)(Y)(CuO2) blocks and the oxidation of Pb2Sr2YCu3O8 does not lead to a superconducting state. Every sample we analyzed should be considered either an oxygen-deficient compound or one containing an excess oxygen with respect to the Pb2Sr2YCu3O9.5 structure.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering