Phase Diagram and Superconductivity of (Ca, Y)(La, Ba)₂Cu₃O_y

Abstract

The samples of (Ca_xY_1-x)(La_xBa_2-x)Cu₃O_y were prepared by firing at 900-950°C in flowing O2 gas. The X-ray diffraction pattern showed that the sample was solved in a single phase of orthorohombic structure with x=0-0.3 and of tetragonal structure with x=0.4-1.0. All the samples showed superconducting transitions between 70K and 95K on both electrical resistivity and magnetic susceptibility. A sharp superconducting transition with ΔT=2K was observed at 80K in the sample with x=1.0, i.e., CaLaBaCu3Oy. In the intermediated composition range, the samples showed broad superconducting transitions with two step drops of resistivity at about 80K and 90K, implying the coexistence of 80K- and 90K-class superconducting phases with a microscopic scales of textures.