Characterization of YBa₂Cu₃O_7−δ Films With Various Porous Structures Grown by Metalorganic Decomposition Route

Metalorganic decomposition route with trifluoroacetates has been successfully used to fabricate YBa2Cu3O7−δ (YBCO)-based coated conductors with an excellent performance. The microstructure and superconducting properties of YBCO films were controlled by the substrate properties and the solution chemistry or by regulating the processing parameters during the film heat treatment. In this work, three YBCO films with various porous structures, namely, a fully dense sample, a cell-structured sample with dense regions surrounded by a porous structure, and a highly porous sample, were deposited on single crystalline substrates (i.e., LaAlO3 and La-doped CeO2 buffered YSZ). The samples were investigated by X-ray diffraction, scanning electron microscopy, a vibrating sample magnetometer, and a magnetooptical imaging technique. All three films show highly epitaxial growth and good superconducting properties (Tc onset around 89 K and .Ic higher than 3 MA/cm2 at 77 K in self-field). However, we found that the porous structures formed by different nucleation and growth mechanisms during the sintering process still have strong influence on the superconducting properties, particularly when applying magnetic fields. The pinning behaviors in the films related to the nanoporous structures, characterized by magnetic moment measurements and visualized by magneto-optical imaging, will be discussed in detail.