SYNTHESIS AND CHARACTERIZATION OF THE SUPERCONDUCTING CUPRATES (PB,CU)SR2(Y,CA)CU2OZ

Single-phase ceramics of superconducting Pb-based layered copper oxides (Pb(1+x)/2Cu(1-x)/2)Sr2(Y1-x)Ca(x))Cu2O2 (x = 0-0.35 and z congruent-to 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 super-conductivity 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.