J_c anisotropy for magnetic field angle in YBCO coated conductor on IBAD-MgO buffered metal tapes

We found that YBCO films deposited by the controlled process showed improved superconducting properties in magnetic fields, even without any artificial pinning centers such as BaZrO₃ and BaSnO₃. The YBCO films with a thickness of 450 nm were deposited on hastelloy tapes with a textured MgO buffer deposited by IBAD (Ion Beam Assist Deposition) method (IBAD-MgO) by PLD method. In the YBCO films on the IBAD-MgO (IBAD-YBCO), the critical current density of 2.9 MA/cm² at 77 K in self-field and the ratio of J_c(B//c)/J_c(B//a, b) at 1 T was almost unity. Furthermore, we found that the J_c anisotropy changed with surface morphology on underlying buffer layer and YBCO thickness. This means that some c-axis correlated pinning centers are included in the films. From the cross-sectional TEM images of the IBAD-YBCO, there were not so many defects such as dislocations, Y₂O₃ inclusions and so on. Thus it is considered that some defects such as oxygen heterogeneity, displacement of a local composition and so on are pinning centers, although such defects can not be detected by a present analytical technique.