Superconducting YBa₂Cu₃O_7-δ thin films with three different orientations

Epitaxial thin films of YBaCuO have been prepared with (1) the a axis perpendicular to (100) SrTiO₃; (2) the c axis perpendicular to (100) SrTiO₃; and (3) the [110] axis perpendicular to (110) SrTiO ₃. Films were fabricated using a multilayer deposition technique involving three electron guns containing Y, BaF₂, and Cu under a pressure of 5×10^-5 Torr of O₂. As deposited films, which contained polycrystalline and amorphous regions, were later annealed in a furnace under a flowing O₂-H₂ O atmosphere. X-ray diffraction patterns as well as scanning electron microscopy and high-resolution electron microscopy images confirm that the films are highly oriented, essentially epitaxial. The a-axis oriented film exhibits zero resistance at 90 K and a critical current density of 2.9×10⁶ A/cm² at 4.2 K while the c-axis oriented film exhibits a T _c of 88 K and a J_c of 0.9×10⁷ A/cm ² at 4.2K; the J_c values were determined magnetically. The [110]-orientation film shows the sharpest transition with a transition width of 1 K and zero resistance at 85 K.