Significantly Improving the Flux Pinning of YBa₂Cu₃O_7- Superconducting Coated Conductors via BaHfO₃ Nanocrystal Addition Using Multistep Film Growth Method

A novel multistep film growth method is developed to prepare high-performance BaHfO3(BHO)-nanocrystal-added YBa2Cu3O7-delta(YBCO) tapes. Upscaled YBCO tapes with high concentrations of 6.2 nm BHO nanocrystals exhibit better self-field and in-field performances when grown by the multistep method compared to those grown by the traditional method. The in-field critical current (I-c) of the 1.6-mu m-thick BHO-added YBCO film at 30 K@3 T is enhanced by 50% in the optimal traditional cases, whereas it is further increased to 180% using a multistep growth strategy. The high-performance YBCO layer is thickened to 2.3 mu m using the multistep method, and the improvement of in-field I-c at 30 K@3 T is enhanced by 215% to 360 A per 4 mm-width compared to the pristine. The BHO size evolution during the high-temperature process reveals that the added nanocrystals coarsened by 4 to 10.5 nm in both the traditional and multistep cases, thereby indicating that the further improvement in performance is attributed to the better film quality grown by the multistep method. This technique can be applied directly to the preparation of scaled REBCO tapes with a length of hundreds of meters.