Synthesis and characterization of the superconducting cuprates (Pb,Cu)Sr2(Y,Ca)Cu2Oz

Abstract

Single-phase ceramics of superconducting Pb-based layered copper oxides (${\mathrm{Pb}}_{(1+\mathit{x})/2\mathrm{}}$ ${\mathrm{Cu}}_{\left(1\mathrm{}\mathrm{-}\mathit{x}\right)/2\mathrm{}}$)${\mathrm{Sr}}_2$ (${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{\mathit{x}}$)${\mathrm{Cu}}_2$ ${\mathrm{O}}_{\mathit{z}}$ (x=0–0.35 and z≃7) are successfully synthesized in an oxidizing atmosphere. The compounds that contain appropriate amounts of Ca (x>0.2) exhibit superconductivity when annealed in air and subsequently quenched into liquid nitrogen. The superconductivity transition temperature increases with increasing x and is raised to 52 K for nearly single-phase samples with x=0.4. It is shown that, when the sample with x=0.35 is quenched, the oxygen content z decreases from 7.10 to 6.99, which is practically equal to the stoichiometric value of 7. It is shown that the length of the a axis is nearly independent of the value of x, being constant at a fixed value for each set of as-sintered and quenched samples and that the a axis of the crystal is shrunken by quenching compared with that of a crystal slowly cooled.