Improvement of epitaxial growth and flux pinning of MOD-derived YBa2Cu3O7−δ nanocomposites films by self-seeding and multi-element doping strategies

YBa2Cu3O7−δ (YBCO) nanocomposite films were fabricated by low-fluorine metal-organic deposition (LF-MOD) route, combining self-seeding and multi-doping strategies with elements of Zr, Hf, Sn and Mn. Under the same growth conditions, due to the self-seeding layer as a template for the c-axis growth of doped films, all the multi-doped films with 200 nm self-seeding layers exhibit good c-axis orientation, even for the heavy doping of 16 mol%. EDS confirmed the four doping elements in the multi-doped YBCO films appear independently, leading to higher density of nano-scale heterogeneous phases than the case of Zr single doping. The pinning force density (Fp) and critical current density (Jc) are improved significantly, which indicates that the optimal doping content is achievable as high as 12 mol% in the case of multi-doping. The multi-12% YBCO films have the highest Fp,max of 6.13 GN/m3 at 77 K, which is about 3.3 times higher than that of the undoped films, and the Jc can reach 4.3 MA/cm2 at 30 K, compared to 3.1 MA/cm2 for the undoped films.