Applications of REBCO coated conductors are now being developed for a very wide range of temperatures and magnetic fields and it is not yet clear whether vortex pinning strategies aimed for high temperature, low field operation are equally valid at lower temperatures and higher fields. A detailed characterization of the superconducting properties of a 15 mol. % Zr-added REBCO thin film made by metal organic chemical vapor deposition, from 4.2 to 77 K under magnetic fields up to 31 T is presented in this article. Even at a such high level of Zr addition, Tc depression has been avoided (Tc = 91 K), while at the same time an exceptionally high irreversibility field Hirr ≈ 14.8 T at 77 K and a remarkably high vortex pinning force density Fp ≈ 1.7 TN/m3 at 4.2 K have been achieved. We ascribe the excellent pinning performance at high temperatures to the high density (equivalent vortex matching field ∼7 T) of self-assembled BZO nanorods, while the low temperature pinning force is enhanced by large additional pinning which we ascribe to strain-induced point defects induced in the REBCO matrix by the BZO nanorods. Our results suggest even more room for further performance enhancement of commercial REBCO coated conductors and point the way to REBCO coil applications at liquid nitrogen temperatures since the critical current density Jc(H//c) characteristic at 77 K are now almost identical to those of fully optimized Nb-Ti at 4 K.

The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba 2 Cu 3 O x film. By a modified MOCVD process, enhanced critical current densities have been achieved with high levels of Zr addition, including 3.83 MA cm −2 in 15 at.% Zr-added 1.1 µm thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/12 mm have been reached in (Gd,Y)BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape, corresponding to a pinning force value of 268 GN m −3 . The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second-phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

Critical current performances of state-of-the-art Zr-added (Gd, Y)BaCuO tapes have been investigated over a temperature range of 20-77 K, in magnetic fields up to 9 T and over a wide angular range of magnetic field orientations. The peak in critical current that is commonly observed in the field orientation perpendicular to the tape in BaZrO 3 (BZO) containing superconducting tapes is found to vanish at 30 K in magnetic fields at 1-9 T. While the critical current of 15% Zr-added tapes was about 40% lower than that of 7.5% Zr-added tapes at 77 K, the pinning force values of the former were found to be 18-23% higher than those of the latter in the temperature range of 20-40 K and in magnetic fields of 3-5 T. The results from this study emphasize the importance of optimization of coated conductor fabrication processes for optimum performance not just in low magnetic fields at 77 K but also at the operating conditions of low temperatures and high magnetic fields that are of interest, especially for rotating superconducting machinery applications.

Critical current (I c ) values of 1384 A/12 mm, corresponding to a critical current density of 12.47 MA cm −2 and a pinning force of 374 GN m −3 , have been achieved at 30 K, 3 T in the orientation of field parallel to the c axis (B c) in (Gd, Y)BaCuO tapes with 15 mol% Zr addition made by metal organic chemical vapor deposition (MOCVD). These tapes show pinning force levels as high as 453 GN m −3 at 30 K. An analysis of the properties of 24-28 (Gd, Y)BaCuO tapes with 15 mol% Zr addition showed a lack of correlation between their critical currents at 30 K, 3 T (B c) and I c values both at 77 K, zero field and at 77 K, 1 T (B c). However, a strong correlation was found between the critical currents at 30 K, 3 T and at 77 K, 3 T (B c). It has also been discovered that the minimum critical current (I c,min ) value at 77 K, 3 T has no influence on the I c,min value at 30 K, 3 T, and it in turn depends on the ratio of the I c values in the orientations of field parallel and perpendicular to the c axis at 77 K, 3 T.

We have conducted a critical current density Jc(T, H) study over a wide temperature T from 77 down to 20 K and a magnetic field H up to 9 T on more than 50 ∼ 0.9 μm-thick REBa2Cu3O7−δ (RE = rare earth) thin films containing different concentrations of BaZrO3 (BZO). We found that, independent of the composition, there is a linear correlation between Jc(77 K, 3 T||c) and Jc(T, H||c) at T down to 20 K and H up to 9 T. Moreover, Jc(77 K, 3 T||c) is also linearly correlated to Jc(T, H||ab) below 40 K. We ascribed this linear correlation to the dominant pinning source of BZO nanorods, which act as a strong correlated pinning at T above ∼30 K and provide weak uncorrelated point pins at lower temperatures. Our result emphasizes that Jc(77 K, 3 T||c) is a key metric for metal-organic chemical vapor deposited REBa2Cu3O7−δ coated conductors.