A comparative study on the flux pinning properties of Zr-doped YBCO film with those of Sn-doped one prepared by metal-organic deposition

We investigated the flux pinning properties of both 10 mol% Zr-and Sn-doped YBa₂Cu₃O_7-δ (YBCO) films with the same thickness of ∽350 nm for a comparative purpose. The films were prepared on the SrTiO₃ (STO) single crystal substrate by the metal-organic deposition (MOD) process. Compared with Sn-doped YBCO film, Zr-doped one exhibited a significant enhancement in the critical current density (J_c) and pinning force density (F_p). The anisotropic J_c,min/J_c,max ratio in the field-angle dependence of J_c at 77 K for 1 T was also improved from 0.23 for Sn-doped YBCO to 0.39 for Zr-doped YBCO. Thus, the highest magnetic J_c values of 9.0 and 2.9 MA/cm² with the maximum F_p (F_p,max) values of 19 and 5 GN/m³ at 65 and 77 K for H // c, respectively, could be achieved from Zr-doped YBCO film. The stronger pinning effect in Zr-doped YBCO film is attributable to smaller BaZrO-3 (BZO) nanoparticles (the average size ≈ 28.4 nm) than YBa₂SnO_5.5 (YBSO) nanoparticles (the average size ≈ 45.0 nm) incorporated in Sn-doped YBCO film since smaller nanoparticles can generate more defects acting as effective flux pinning sites due to larger incoherent interfacial area for the same doping concentration.