CRYSTAL-STRUCTURE OF THE SUPERCONDUCTOR PB2SR2-XLAXCU2O6+DELTA

The crystal structure of Pb2Sr(2-x)La(x)Cu2O6+delta with x = 1.0 has been determined by Rietveld refinement from X-ray powder diffraction data. The unit cell is orthorhombic, space group Pman, with lattice parameters a = 5.3119(4) angstrom, b = 5.4140(4) angstrom and c = 12.629(1) angstrom. The copper atoms in the CuO2 planes lie in octahedra elongated along the c-direction, with two oxygens slightly above and two others slightly below these planes. In these octahedra the copper atoms are randomly distributed over two positions with z = 0.020(1) and z = -0.020(1), respectively. A remarkable feature of this compound is the 2-coordination of the Cu(1) atoms in between the PbO layers. The orthorhombic distortion is reflected in the relatively large deviation from the value 1/2 of the y-coordinate of the oxygen atoms in the PbO layers.