Influence of artificial pinning centers on structural and superconducting properties of thick YBCO films on ABAD-YSZ templates

Recent efforts in the development of YBa₂Cu₃O_7−x (YBCO) coated conductors are devoted to the increase of the critical current I _c in magnetic fields. This is typically realized by growing thicker YBCO layers as well as by the incorporation of artificial pinning centers. We studied the growth of doped YBCO layers with a thickness of up to 7 μm using pulsed laser deposition with a growth rate of about 1.2 nm s⁻¹. Industrially fabricated ion-beam textured YSZ templates based on metal tapes were used as substrates for this study. The incorporation of BaHfO₃ (BHO) or Ba₂Y(Nb_0.5Ta_0.5)O₆ (BYNTO) secondary phase additions leads to a denser microstructure compared to undoped films. A purely c-axis-oriented YBCO growth is preserved up to a thickness of about 4 μm, whereas misoriented texture components were observed in thicker films. The critical temperature is slightly reduced compared to undoped films and independent of film thickness. The critical current density J _c of the BHO- and BYNTO-doped YBCO layers is lower at 77 K and self-field compared to pure YBCO layers; however, I _c increases up to a thickness of 5 μm. A comparison between films with a thickness of 1.3 μm revealed that the anisotropy of the critical current density J _c(θ) strongly depends on the incorporated pinning centers. Whereas BHO nanorods lead to a strong B∣∣c-axis peak, the overall anisotropy is significantly reduced by the incorporation of BYNTO forming a mixture of short c-axis-oriented nanorods and small (a–b)-oriented platelets. As a result, the J _c values of the doped films outperform the undoped samples at higher fields and lower temperatures for most magnetic field directions. (paper)