The preparation of high- J _c Gd_0.5Y_0.5Ba₂Cu₃O_7−δ thin films by the MOCVD process

A home-designed metal organic chemical vapor deposition (MOCVD) system has been employed to prepare high critical current density (J_c) Gd_0.5Y_0.5Ba₂Cu₃O_7−δ (GdYBCO) thin films on LaMnO₃/epitaxial MgO/ion beam assisted deposition (IBAD)-MgO/solution deposition planarization (SDP)-Y₂O₃-buffered Hastelloy tapes; the thin films were directly heated by the Joule effect after applying an heating current (I_h) through the Hastelloy tapes. The effect of the mole ratio of the metal organic sources has been systematically investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated that the GdYBCO films crystallized better and became denser with the increasing of the Cu/Ba ratio from 1.0 to 1.1, yielding a J_c at 77 K and 0 T of 200 nm GdYBCO film increasing from 2.5 MA cm⁻² to 7 MA cm⁻². In addition, SEM and energy dispersive spectrometer (EDS) characterizations revealed that more and more outgrowths appeared and the density of the film was reduced with an increase in the Cu/Ba ratio from 1.1 to 1.2. When the I_h was 26.8 A and the mole ratio of Gd(tmhd)₃, Y(tmhd)₃, Ba(tmhd)₂ and Cu(tmhd)₂ in the precursor was 0.55:0.55:2:2.2, the critical current (I_c) of the deposited 200 nm-thick GdYBCO film reached a 140 A cm⁻¹ width (77 K, 0 T), corresponding to the J _c 7 MA cm⁻² (77 K, 0 T). (paper)