Thickness Dependence of Structural and Superconducting Properties of Single-Crystal-Like GdBCO Films Prepared by Photo-Assisted MOCVD

High-quality GdBa₂Cu₃O_7-δ (GdBCO) films with thicknesses of 0.14-1.62 μm were deposited on (100)-oriented LaAlO₃ substrates by photo-assisted metal-organic chemical vapor deposition technique. Evaluation of film microstructure and strain-relaxation phenomenon in the growing films and their effects on the crystallographic and superconducting properties of the GdBCO films have been investigated. A single-crystal-like cross-sectional morphology with dense and crack-free surface and no grain boundary visible was observed. The c-axis lattice parameters of the GdBCO films grown with different thicknesses were used to determine the out-of-plane strain. The result shows that the strain could be gradually relieved as film thickness increases. Highly biaxially textured GdBCO films have been obtained. For a 0.31-μm GdBCO film sample, the full-widths at half-maximum were 0.08° and 0.47° for out-of-plane and in-plane orientations, respectively. Such low values were similar to that of single-crystal GdBCO. The highest critical current density (J_c) value is ~ 2.5MA/cm² (77 K and 0 T). As films were getting thicker, their J_c values decrease gradually. This is mainly attributed to a lack of pinning centers in the thicker films.