Engineering current density over 5 kA mm −2 at 4.2 K, 14 T in thick film REBCO tapes To cite this article: Goran Majkic et al 2018 Supercond. Sci. Technol. 31 10LT01 View the article online for updates and enhancements. Related content Critical current density above 15 MA cm2 at 30 K, 3 T in 2.2 m thick heavily-doped (Gd,Y)Ba2Cu3Ox superconductor tapes V Selvamanickam, M Heydari Gharahcheshmeh, A Xu et al.-Sample and length-dependent variability of 77 and 4.2 K properties in nominally identical RE123 coated conductors L Rossi, X Hu, F Kametani et al.-Requirements to achieve high in-field critical current density at 30 K in heavilydoped (Gd,Y)Ba2Cu3Ox superconductor tapes V Selvamanickam, M Heydari Gharahcheshmeh, A Xu et al.-Recent citations Goran Majkic-Correlation of In-Field Performance of Thick REBCO Films Between 0-14 T and 4.2-77 K Goran Majkic et al-Effect of Deposition Temperature on Microstructure and Critical Current Properties of Zr-Doped GdYBCO Superconducting Tapes Made by MOCVD Ziming Fan et al

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An Advanced MOCVD (A-MOCVD) reactor was used to deposit 4.8 µm thick (Gd,Y)BaCuO tapes with 15 mol% Zr addition in a single pass. A record-high critical current density (Jc) of 15.11 MA/cm2 has been measured over a bridge at 30 K, 3T, corresponding to an equivalent (Ic) value of 8705 A/12 mm width. This corresponds to a lift factor in critical current of ~11 which is the highest ever reported to the best of author’s knowledge. The measured critical current densities at 3T (B||c) and 30, 40 and 50 K, respectively, are 15.11, 9.70 and 6.26 MA/cm2, corresponding to equivalent Ic values of 8705, 5586 and 3606 A/12 mm and engineering current densities (Je) of 7068, 4535 and 2928 A/mm2. The engineering current density (Je) at 40 K, 3T is 7 times higher than that of the commercial HTS tapes available with 7.5 mol% Zr addition. Such record-high performance in thick films (>1 µm) is a clear demonstration that growing thick REBCO films with high critical current density (Jc) is possible, contrary to the usual findings of strong Jc degradation with film thickness. This achievement was possible due to a combination of strong temperature control and uniform laminar flow achieved in the A-MOCVD system, coupled with optimization of BaZrO3 nanorod growth parameters.

We present results on the in-field critical current (I c ) performance of 4.0 µm thick REBCO film with 15% Hf addition with fields up to 31.2 T and field orientations in the B∥ab plane and B∥c axis. Unlike the behavior at B∥c, the critical current at B∥ab is only very weakly dependent on field, decreasing from self-field to 31.2 T by only 22%, i.e. from the self-field value of ∼7700 A/4 mm width to ∼6300 and 5812 A/4 mm width at 14 and 30 T, respectively. These values are remarkably 3 and 5.7x higher than the corresponding critical currents at B∥c. The in-field behavior of the present 15% Hf sample at field orientation B∥c axis is nearly identical to the previously reported record values found in 4.3 and 4.6 µm thick 15% Zr samples in terms of critical current density. In contrast to the pinning force behavior in the B∥c orientation, which saturates to a constant value of 1.7 TN m −3 above ∼5-6 T, the pinning force in the B∥ab orientation increases near-linearly, reaching a remarkable value of over 11.5 TN m −3 at 31.2 T. These results demonstrate the potential of thick REBCO conductors at 4.2 K for high field and energy density applications, in particular where the magnetic field is contained near the ab-plane.

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We report on strain and composition effects associated with growth of self-assembled BaZrO 3 (BZO) nanorods in REBa 2 Cu 3 O 7−δ (REBCO) superconductors (RE = rare earth = Y and Gd), which have a profound effect on flux pinning and in-field critical current performance. The a-b plane mismatch between BZO and REBCO is never fully coherently accommodated. Instead, the nanorods always assume a size at least one unit cell smaller than the corresponding 'hole' in the REBCO matrix, thus providing deep minima of in-plane mismatch strain. Next, we show that the nominal BZO nanorods are in fact solid solution Ba 2+ (Zr 4+ 1−z RE 3+ z )O 3−δ perovskite, thus strongly affecting the stoichiometry and relative amounts of REBCO and BZO. We demonstrate that by varying only the Ba content in the nominal composition of 15 mol.% BZO + REBCO, the unit cell density of BZO can be tuned from 5% to 23%, and the linear density of RE 2 O 3 (REO) precipitates from 18 to 1 µm −1 . The results explain the wide range of pinning performances observed for the same nominal amount of Zr addition and provide insight into the mechanisms behind the complex phenomenon of growth of nanorods by self-assembly in REBCO superconductors.

The critical current and pinning mechanisms at 4.2 K have been studied over a magnetic field range of 0-14 T for Zr-added (0, 5 and 15 mol.%) REBa 2 Cu 3 O 7-x (REBCO and RE = rare earth) coated conductors fabricated by advanced metal organic chemical vapor deposition (A-MOCVD). It is found that the (Ba + Zr)/Cu content in Zr-added (5 and 15 mol.%) REBCO affects the critical current at 77 K, 0 T as well as density, continuity and shape of BaZrO 3 (BZO) self-assembled nanocolumns and RE 2 O 3 in-plane precipitates that significantly enhance the pinning force density Fp(H) as well as isotropic pinning landscape at 4.2 K. In addition to bell-shape dependence of critical current density, J c , at 4.2 K with (Ba + Zr)/Cu content we observed an unusual Fp(H) behavior correlated to particular type of pinning centers, morphology and distribution that have been revealed by TEM microstructure analysis. By fitting the Dew-Hughes equation of the pinning force density Fp(H) at 4.2 K we extract the scaling behaviors of the Fp(H) associated with the competition of pinning mechanisms driven by vertically-aligned BZO nanorods and in-plane RE 2 O 3 pinning defects. This result sheds light on approaches towards interactive control of strong and isotropic pinning centers in Zr-added REBa 2 Cu 3 O 7-x (REBCO and RE = rare earth) coated conductors, and especially understanding the correlation between microstructural characteristics and vortex pinning mechanisms at 4.2 K in high magnetic fields.

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