Co-doping with BaSnO₃ and BaHfO₃ by ultra-high rate PLD enabling formation of high-density nanocolumns in EuBa₂Cu₃O_7-<i>δ</i> films

Abstract Introduction of artificial pinning centers through defects engineering is an effective strategy to mitigate the reduction of the in-field current carrying capacity of REBa 2 Cu 3 O 7− δ (REBCO) tapes. However, it is a challenge to form high-density columnar secondary phases while maintaining the high crystallinity of REBCO under high-speed deposition during the pulsed laser deposition (PLD) process, which restricts the mass production of high-performance tapes for high-field magnet applications. In this work, a BaHfO 3 + BaSnO 3 co-dopant strategy was utilized to modulate the microstructure of doped EuBa 2 Cu 3 O 7− δ (EuBCO) films via reel-to-reel PLD with ultra-high deposition rate (exceeding 100 nm s −1 ). These nanocolumnar structures, composed of BaSn x Hf 1 − x O 3 (BSHO) at the atomic scale, are aligned along the thickness direction throughout the EuBCO layer. The high-density nanocolumns, ∼5 nm diameter, exhibited an areal density of about 2200 pieces μ m −2 . This unique microstructure significantly enhanced the in-field J c of the co-doped film. At 50 K and 3 T, the J c reaches ∼4.0 MA cm −2 in the perpendicular field, exceeding that in the parallel field. Notably, even under a higher field (50 K and 8 T), the J c ( θ ) curve of the co-doped film exhibits a pronounced correlated pinning peak in the perpendicular field. The large in-plane lattice mismatch between the BSHO and EuBCO leads to the formation of semi-coherent interfaces, which introduce numerous nanoscale defects acting as random pinning centers under high fields. High-field superconductivity measurement results indicate that the pinning force displays a non-saturation phenomenon at 4.2 K up to 24 T, achieving a high value of ∼990 GN m −3 .