Optimization of annealing parameters for the growth of epitaxial Ba2YCu3O7−x films on LaAlO3(100)

Abstract

The superconducting and structural properties of Ba₂YCu₃O_7−x (BYCO) films on LaAlO₃(100) substrates can be improved by carefully optimizing the post‐deposition annealing parameters. Films are grown by co‐deposition of BaF₂, Y, and Cu in the correct stoichiometric ratio to within 1% of 2:1:3. Annealing parameters in an ex situ furnace, including the ambient, annealing temperature, oxidation temperature, and duration of anneals are systematically studied. Films are characterized for epitaxial quality (χ_min), morphology, critical temperature (T_c), sharpness of the superconducting transition (ΔT), and critical current density (J_c). For example, beyond simply dissociating BaF₂, the use of wet O₂ appears to prevent the agglomeration of oxides during the initial heating process, and then act to thermodynamically stabilize the basic BYCO film structure at high temperatures after being formed. Comparisons are made with the best single‐crystal BYCO structural and electrical data available. The optimized films have relatively smooth morphology with χ_min90 K, ΔT10⁶ A/cm² in essentially zero magnetic field at 77 K.