Enhanced flux pinning through high levels of Zr addition in Gd 0.5 Yb 0.5 Ba 2 Cu 3 O 7− δ superconducting tapes

Abstract The effects of Zr doping on the microstructure and low-temperature critical current performance of Gd 0.5 Yb 0.5 Ba 2 Cu 3 O 7− δ (Gd 0.5 Yb 0.5 BCO) tapes fabricated by metal–organic chemical vapor deposition have been systematically investigated. Zr doping in Gd 0.5 Yb 0.5 BCO films facilitates the formation of elongated BaZrO 3 nanorods while suppressing the growth of dense, vertically aligned BaCuO 2 nanorods. At Zr doping concentrations exceeding 10 mol%, BaCuO 2 nanorods barely self-assemble in the films; instead, the flux-pinning landscape in these heavily Zr-doped films transforms entirely into an array of BaZrO 3 nanorods, with number densities of 1.4 × 10 3 and 2.2 × 10 3 nanorods µ m −2 at 15 and 25 mol% Zr contents, respectively. This microstructural evolution drives distinct variations in the critical current characteristics of Gd 0.5 Yb 0.5 BCO tapes with different Zr doping levels. Specifically, 5, 10, 15, 20 and 25 mol% Zr additions enhance the critical current performance at 4 K over magnetic field ranges of 0–17.3 T, 0–10.5 T, 0–13.4 T, 0–15.1 T and 0.3–20.5 T, respectively. This magnetic-field dependent critical current behavior is presumably correlated with the synergistic or exclusive presence of BaCuO 2 and BaZrO 3 nanorods in the flux-pinning landscape, whose low temperature pinning properties are analyzed via microstructure characterization and critical current measurements. This study demonstrates that heavy Zr doping (15–25 mol%) in Gd 0.5 Yb 0.5 BCO films constitutes an effective strategy to significantly enhance critical current performance over a broad low-to-medium magnetic field range at low temperatures. In contrast, flux pinning by a high density of intrinsic BaCuO 2 nanorods in undoped Gd 0.5 Yb 0.5 BCO films underlies superior critical current performance in ultra-high magnetic fields (>20 T).