Crystal Structure of the High Tc Superconductor LnBa2Cu3O7-δ (Ln=Sm, Eu and Gd)

The crystal structure of the high Tc superconductor LnBa2Cu3O7-δ (Ln=Sm, Eu and Gd) has been determined by Rietveld analysis of X-ray powder diffraction data. The compounds crystallize in an oxygen-deficient layered perovskite structure with space group Pmmm. The structure is isomorphic with YBa2Cu3O7-δ. The Ln and Ba atoms have an ordered arrangement, oxygen on a z=1/2 plane is missing and the oxygen site on the basal Cu plane is selectively occupied.