High Critical Current Density and Enhanced Pinning in Superconducting Films of YBa₂Cu₃O_7−δ Nanocomposites with Embedded BaZrO₃, BaHfO₃, BaTiO₃, and SrZrO₃ Nanocrystals

Chemical solution deposition (CSD) of YBa2Cu3O7−δ (YBCO) nanocomposites from colloidal precursor solutions containing double metal oxide preformed nanocrystals is a promising, cost-effective, and reproducible approach to producing superconducting films with high critical current density (Jc) and enhanced pinning. Here, the influence of the preformed nanocrystal composition on the microstructure and superconducting properties of the YBCO nanocomposite films is studied, with a focus on establishing a simple and scalable process to grow nanocomposites that can be transferred to grow nanoadded coated conductors. Colloidal stable BaZrO3, BaHfO3, BaTiO3, and SrZrO3 nanocrystals (3–6 nm diameter) were synthesized and added to an environmentally friendly low-fluorine YBCO precursor solution. High-quality superconducting layers were grown on LaAlO3 single-crystal substrates from these four nanocomposite precursor solutions in a single deposition process, without the need of a seed layer, yielding self-field Jc of 4–5 MA/cm2 at 77 K. The different YBCO microstructures produced by the four types of nanocrystals and the resulting microstrain of the films are compared and related with the magnetic-field and angular dependence of Jc. We demonstrate the BaHfO3-containing nanocomposite as the best-performing with a homogeneous distribution of nanoparticles with 7 nm average diameter and a high density of stacking faults, which leads to some of the best superconducting properties ever achieved via low-fluorine CSD. Jc exhibits a much smoother decay in the applied magnetic fields and a much more isotropic behavior for nonparallel magnetic fields, and the pinning force is increased by a factor of 3.5 at 77 K and 1 T with respect to the pristine film.