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Oxygen annealed YBCO samples were treated with oxygen plasma at room temperature. After plasma treatment for 40 minutes, the value of Tc increases from 92 K to 96.0 K. The curves of real ac susceptibility showed that superconducting component in YBCO increased after plasma treatment for 40 minutes. It is believed that all these were caused by oxygen cations. It is suggested that oxygen plasma at room temperature could inject some oxygen atoms in b axis, to make Cu(1)-O chains more complete in the surface layer, leading to the increase in Tc.

The nominal composition of La1.85Sr0.15Cu1−yMgyO4superconductors with 0.00≤y0.30 are synthesized by the solid state reaction techniques. The structure of these Mg doped samples is characterized by X-ray diffraction studies. The atomic structure parameters are obtained by Rietveld refinements. Some meaningful bond distances are determined according to the refined results. The distance between the two apical oxygen atoms in the CuO6octahedra changed with the Mg content. The room temperature resistivity for each sample is measured.

YBa2(Cu1−yCoy)3Oxsuperconductors with 0.02≤y≤0.04 are prepared by the convensional techniques. The content of oxygen increases with the increase of Co concentration. The structures of these samples are characterized by neutron abd X-ray powder diffraction studies. Two phases, orthorhombic and tetragonal ones, co-exist in sample with y=0.03.

Crystal structures of LaBa2Cu3−xFexOywith 0.0 ≤ rmx ≤ 0.25 shows an anomalous structural phase transition depending on Fe contents. With Fe content increasing the structure varies in the form of orthorhombic-to-tetragonal phases and then regeneration of orthorhombicity from tetragonal phase, which is observed from the separation or overlap of (0 2 0) and (2 0 0) lines in the X-ray diffractograms. Variation of lattice constants a, b and c with Fe content also supports by the anomalous phase transition.