OPTIMIZATION OF ANNEALING PARAMETERS FOR THE GROWTH OF EPITAXIAL BA2YCU3O7-X FILMS ON LAALO3(100)

The superconducting and structural properties of Ba2 YCu3O7-x films on LaA1O3 (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 (chi-min), morphology, critical temperature (T(c)), sharpness of the superconducting transition (DELTA-T), 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 chi-min < 3%, T(c) > 90 K, DELTA-T < 0.5 K, and J(c) > 10(6) A/cm2 in essentially zero magnetic field at 77 K.