Formation of Self-Assembled, Double-Perovskite, Ba2YNbO6 Nanocolumns and Their Contribution to Flux-Pinning and $J_{\text{c}}$ in Nb-Doped YBa2Cu3O7-\delta Films

Ba 2 RENbO 6 (RE = rare earth elements including Y) compounds are considered new additives for superior flux-pinning in YBa 2 Cu 3 O 7-\delta (YBCO) films due to their excellent chemical inertness to and large lattice mismatches with YBCO. Simultaneous laser ablation of a YBCO target and a Nb metal foil attached to the surface of the target resulted in epitaxial growth of YBCO films having columnar defects comprised of self-aligned Ba 2 YNbO 6 (BYNO) nanorods parallel to the $c$-axis of the film. Compared to pure YBCO, YBCO+BYNO films exhibited no $T_{\text{c}}$ reduction as well as superior $J_{\text{c}}$ performance with higher self- and in-field $J_{\text{c}}$ by a factor of 1.5--7 and also exhibited a strong $J_{\text{c}}$ peak for $H\parallel c$ indicative of strong $c$-axis correlated flux-pinning.