Large domain YBa2 Cu3 07-δ/2BaCuO5 (YBCO) samples were prepared by top-seeded melt-textured process, with the addition of SnO2 and CeO2 or PtO2. It was found that, in comparison to that in the CeO2-doped sample, the YBa2 Cu3 O7-δ(123) matrix was twisted in the PtO2-doped sample and its Y2BaCuO5 (211) particles were larger on average and less homogeneously distributed. The PtO2-doped sample showed a more obvious second-peak effect, and higher values of a-b plane critical current density (3Jcab) and irreversibility fields (Bt,,). The enhancement of3 Jcab is related to the microstructure inhomogeneity and the core surface AK pinning.

The recent observation of superconductivity above 160 K under high pressures has prompted us to investigate the possibility of retaining such high-temperature superconductivity at ambient pressure by substituting Sr for Ba in Hg Ba2 Caz Cu3 08 (Hg-1223). High-purity (≥ 90%) Hg-1223 phase samples were synthesized with a nominal composition of Hgz Srx Ba2_x Caz Cu3 O8+& (where z=0.75 and x=0.0.5 or 1). By adding a second element, Pb or Mo, supposedly to the Hg site, (Hg, Pb/Mo)Sr2 Caz Cu3 O8+& with purity up to 90% was achieved. Unfortunately, Tc decreases with Sr substitution. The roles of Sr in the phase stability, and the synthesis conditions of the Sr based Hg-1223, and the Sr substitution effect on the Tc of these samples will be discussed.