It is reported that Ca-doping can improve the weak links between grain boundaries and increase the critical current density Jc of YBa2 Cu3 O7d polycrystalline films [Phys. Rev. B 58 (1998) 9543; Nature 407 (2000) 162]. In this paper, we investigated the preparation and superconducting properties of YBa2Cu3O7 d (YBCO) and Y1x Cax Ba2 Cu3 O7d (x=0.05, 0.1, and 0.2) (YCBCO) coatings on yttrium stabilized zirconia (YSZ) single crystal substrates by powder melting growth process. The X-ray diffraction (XRD) indicated that: (1) the coatings were of YBa2 Cu3 O7 d (Y123) phase with c-rientation; (2) the Y2 Ba Cu O5 (Y211) phase remained clearly in the YBCO coating, but much less in the YCBCO coatings. The effect of Ca-doping on the formation of the Y211 phase was analyzed with the help of the differential thermal analysis (DTA). The results of R-T and I-V relationship at 77K demonstrated that the zero resistance temperature Tc0 decreased with the Ca content, while the critical current density Jc (77K) was improved for x=0.05.

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.