The structure and superconductivity of Y1−xCaxBa2Cu3O7−δ coatings on YSZ single crystal substrate

It is reported that Ca-doping can improve the weak links between grain boundaries and increase the critical current density J c of YBa 2 Cu 3 O 7− δ polycrystalline films [Phys. Rev. B 58 (1998) 9543; Nature 407 (2000) 162]. In this paper, we investigated the preparation and superconducting properties of YBa 2 Cu 3 O 7− δ (YBCO) and Y 1− x Ca x Ba 2 Cu 3 O 7− δ ( 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 YBa 2 Cu 3 O 7− δ (Y123) phase with c -orientation; (2) the Y 2 BaCuO 5 (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 77 K demonstrated that the zero resistance temperature T c0 decreased with the Ca content, while the critical current density J c (77 K) was improved for x = 0.05.