Crystal Structure of the High Tc Superconductor YbBa2Cu3O7-δ

Abstract

The crystal structure of the high T _c superconductor YbBa₂Cu₃O_7-δ is determined by Rietveld analysis of X-ray powder diffraction data. The crystal system is orthorhombic (space group Pmmm) with lattice parameters a=3.8710(2) Å, b=3.8018(2) Å and c=11.6576(5) Å. The structure is isomorphic with YBa₂Cu₃O_7-δ. The layered perovskite structure with the tripled c-axis exhibits ordering of Yb and Ba, an oxygen-deficient Yb layer at z=1/2 and preferential oxygen occupation on the basal Cu plane. The compound shows superconductivity at 90 K (midpoint) with the transition width of 3.0 K.