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

Abstract

Recent efforts in the development of YBa2Cu3O7−x (YBCO) coated conductors are devoted to the increase of the critical current Ic 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(Nb0.5Ta0.5)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 Jc of the BHO- and BYNTO-doped YBCO layers is lower at 77 K and self-field compared to pure YBCO layers; however, Ic 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 Jc(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 Jc values of the doped films outperform the undoped samples at higher fields and lower temperatures for most magnetic field directions.