Crystal structure of superconducting BaPb0.7Bi0.15Sb0.15O3

Neutron powder diffraction data have been used to investigate the structure of superconducting BaPb0.7Bi0.15Sb0.15O3 (T-c = 5.3 K). The Rietveld profi le refinement has shown that it is tetragonal, space group I4/mcm, with the lattice parameters of a = 6.0405(1) Angstrom and c = 8.5812(3) Angstrom. B aPb0.7Bi0.15Sb0.15O3 consists, thus, of disordered arrangement of ph, Bi an d Sb atoms with the averaged (Pb,Bi,Sb)-O distance of 2.155 Angstrom. Its s tructure can be viewed as distortion of the ideal cubic perovskite by the c ooperative tilt of (Pb,Bi,Sb)O-6 octahedra along the primitive [001](p) axi s (similar to6.7 degrees), as was previously observed for the superconducti ng phase in the BaPb1-xBixO3 system. (C) 2001 Elsevier Science Ltd. All rig hts reserved.