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 (Tc=5.3 K). The Rietveld profile refinement has shown that it is tetragonal, space group I4/mcm, with the lattice parameters of a=6.0405(1) Å and c=8.5812(3) Å. BaPb0.7Bi0.15Sb0.15O3 consists, thus, of disordered arrangement of Pb, Bi and Sb atoms with the averaged (Pb,Bi,Sb)–O distance of 2.155 Å. Its structure can be viewed as distortion of the ideal cubic perovskite by the cooperative tilt of (Pb,Bi,Sb)O6 octahedra along the primitive [001]p axis (∼6.7°), as was previously observed for the superconducting phase in the BaPb1−xBixO3 system.