Neutron powder diffraction study of Pb2Sr2YCu3O8, the prototype of a new family of superconductors

Abstract

Abstract The structure of Pb 2 Sr 2 YCu 3 O 8 has been analyzed with powder neutron diffraction techniques and profile analysis. The results of this study confirm the general structural features determined by X-ray single-crystal methods. The material has pseudo tetragonal symmetry, but is orthorhombic, space group Cmmm with lattice parameters a =5.3933(2), b =5.4311(2), and c =15.7334(6)A. The orthorhombic distortion is caused by the disordering in the ab plane of the oxygen atoms of the PbO layers over the general position of the space group, with x =0.275(5) and y =0.402(5) A. The structure of this compound can be derived from that of YBa 2 Cu 3 O 6 by substituting the Cu layers with blocks of … PbO.Cu.PbO… . Of the two Cu atoms in the asymmetric unit, one has two fold coordination while the other has five fold pyramidal coordination with the apex elongated along the c -axis.