Characterization and synthesis of Y0.9Ca0.1Ba1.8Sr0.2Cu3O7−δ via combining sol–gel and solid-state route

We applied the conventional sol–gel and solid-state reactions in this study to prepare double-substituted superconducting Y0.9Ca0.1Ba1.8Sr0.2Cu3O7−δ. The result and the effect of calcium and strontium doping on high-Tc compound Y-123 have been investigated. The precursor gel Ca–Ba–Sr–Cu–O was prepared by acetate–tartrate sol–gel route which involved hydrolysis and olation (polycondensation). Y0.9Ca0.1Ba1.8Sr0.2Cu3O7−δ was obtained by solid-state reaction between Y2O3 and Ca–Ba–Sr–Cu–O heated at 880 °C for 18 h with step cooling 50 °C/h until 450 °C. Without oxygen flow during the whole annealing process, the sample still showed good superconducting properties with Tc-zero close to 80 K. The presence of organic material in the sol–gel precursor Ca–Ba–Sr–Cu–O is nucleophile species, which is chemically reactive to Y2O3 during solid-state reaction thus enhance the diffusion rate. Moreover, –OH group in the precursor gel has ability to provide a sufficient amount of oxygen for the sample to stabilized the multicomponent superconductor.