Crystal Structure of the Superconductor Ba1.8Nd1.2Cu₃O7-y

The structure parameters of a superconductor with the nominal composition Ba 1.8 Nd 1.2 Cu 3 O 7- y were refined by the Rietveld analysis of TOF neutron powder diffraction data. This material is tetragonal with lattice constants a =3.8919 Å and c =11.6811 Å and isomorphous with Ba 1.5 La 1.5 Cu 3 O 7± y with an oxygen-deficient triperovskite structure. An oxygen site at (0, 1/2, 0) is 49% occupied, the Nd 3+ ion at (1/2, 1/2, 1/2) is coordinated to eight oxide ions, and a metal site at (1/2, 1/2, 0.1842) is 90% and 10% occupied by Ba 2+ and Nd 3+ ions, respectively.