Biaxial alignment control of YBa₂Cu₃O_7−x films on random Ni-based alloy with textured yttrium stabilized-zirconia films formed by ion-beam-assisted deposition

Biaxially aligned YBa₂Cu₃O_7−x (YBCO) films were fabricated on random Ni-based alloy tapes with yttrium stabilized-zirconia (YSZ) buffer layers deposited by ion-beam-assisted deposition (IBAD). Ar⁺ ion bombardment was found to have two significant effects on the crystalline structure of the YSZ buffer layers: to align a [100] axis with the substrate normal and a [111] axis with the bombarding beam axis. The resulting YSZ films were biaxially aligned on the random polycrystalline tapes, and the azimuthal distribution of the a- and b-axes of YBCO films on the top of the YSZ films was restricted to 10° FWHM. A critical current density (J_c) of 1.13 × 10⁶ A/cm² (77 K, 0 T) was obtained, and 1.1 × 10⁵ A/cm² was maintained at 5 T (77 K, B⊥c). The existence of both intrinsic and extrinsic pinning properties was clearly observed in the angular dependence of J_c with B⊥I. The longitudinal field effect on J_c was clearly observed, which indicated straight transport currents. This is evidence for strongly coupled current paths that demonstrate the bulk pinning properties of YBCO.