Microstructural characterization and superconducting properties of GdBa2Cu3O7-x films prepared by a fluorine-free sol-gel process

Abstract This work presents a promising method to fabricate fluorine-free GdBa2Cu3O7-x (GdBCO) films on LaAlO3 (LAO) substrate using a sol-gel technique. The phase transformation during the fabrication process and the influence of sintering parameters including crystallization temperature and oxygen partial pressure on the microstructure and superconductivity were investigated by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The c-axis oriented microstructure of GdBCO films was obtained under the crystallization temperature of 820 °C and oxygen partial pressure of 1.16%. The barium-containing BaCO3 phase can transform into Ba(OH)2, which contributed to the formation of fluorine-free GdBCO. Moreover, scanning transmission electron microscope characterization revealed that stacking defects were formed near the LAO substrate and spread throughout the whole GdBCO matrix with weak superconductivity regions, which acted as effective pinning centers to inhibit flux creep. This resulted in a stronger current-carrying capacity of the GdBCO film than that of YBa2Cu3O7-x (YBCO) film. Finally, a sustainable GdBCO film with the superconducting transition temperature (Tc) of 90 K and the critical current density (Jc) of 1.23 MA/cm2 (77 K, 0 T) was achieved through a simple and effective fluorine-free sol-gel method.