EFFECT OF ANNEALING UNDER HIGH OXYGEN-PRESSURE ON THE STRUCTURE AND SUPERCONDUCTIVITY OF (BA0.85ND0.15)2NDCU3O6+Z

The superconducting properties of (Ba0.85Nd0.15)2NdCu3O6+z were improved by annealing at 350°C under an oxygen pressure of 100 MPa. Tc of the as-grown sample was 33.0 K and that of the oxidized sample was 54.1 K. Crystal structures of as-grown and oxidized samples were refined by Rietveld analysis of TOF neutron diffraction data. They are isomorphous with tetragonal Ba2YCu3O6+z, and contain CuOz sheets which act as charge reservoirs to dope holes on CuO2 sheets. Oxygen is intercalated in an O(1) site on the CuOz sheet by annealing. The occupation probability of this oxygen site affects the superconducting properties in a striking manner. The Cu and O atoms on the CuOz sheets and the O atom on the (Ba0.85Nd0.15)O sheets are displaced from the ideal positions, which is due to the substitution of small Nd3+ ions for large Ba2+ ions. © 1990.