Synthesis, crystal structures and superconductivity of new copper oxyfluorides, Sr2RCu2O5F (R = Y,La,Nd,Sm,Gd,Dy,Er and Yb)

Article abstract of DOI:10.1016/0921-4534(96)00430-3

A new series of oxyfluoride compounds, Sr₂RCu₂O₅F (R = Y,La,Nd,Sm,Gd,Dy,Er and Yb), was successfully synthesized under high pressure of 6 GPa. Electron microscopic observation and X-ray Rietveld analysis indicated that they are essentially isostructural to La₂SrCu₂O₆ (tetragonal, I4/mmm) with a half of apical oxygen sites of CuO₅ pyramids replaced by F atoms. Superconductivity occurred in the Nd analogue after Ca substitution for x > 0.5 in Sr₂Nd_1-xCa_xCu₂O₅F. A single-phase sample of the Nd analogue was obtained at x = 0.8 having the highest T_c of 85 K with a Meissner fraction of 6.8% and a shielding fraction of 7.4% at 5 K. These small fractions suggest a small grain size, weak intergrain coupling and/or weak pinning force.