Crystallization Mechanism of Nd1+xBa2−xCu3O7−y and YBa2Cu3O7−y Films Deposited by Metalorganic Deposition Method Using Trifluoroacetates

Abstract

YBa₂Cu₃O_7−y(Y123) and Nd_1+xBa_2−xCu₃O_7−y (Nd123) films were deposited by the metalorganic deposition method, and the growth mechanism of these films was investigated by high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. The Y123 and Nd123 films were prepared by spin-coating LaAlO₃ (001) and SrTiO₃ (STO) (001) substrates, respectively, with solutions including trifluoroacetates. Then, the samples were heat treated at 673 K in a humid O₂ gas flow to form amorphous precursor films. Finally, the precursor films were heated at higher temperatures for 0–30 min in a humid Ar/O₂ gas flow and cooled rapidly from those annealing temperatures. It was found that CuO crystals with a size of 10–20 nm are segregated in the Y123 and Nd123 amorphous precursor films. In the Y123 quenched film prepared by cooling the precursor film rapidly after the heat-treatment at 1048 K for 30 min, a polycrystalline film including Y₂Cu₂O₅, BaF₂, and CuO crystals was found to be generated on the c-axis-oriented Y123 film. In contrast, in the Nd123 quenched films, (NdBa)₂CuO₄(Nd201) phase was found to be formed first on the surface of the STO substrate. In conclusion, the c-axis-oriented Y123 film is formed by diffusion and reaction of Y₂Cu₂O₅, BaF₂, and CuO crystals, and the Nd201 phase reacts with BaF₂ and CuO crystals in a humid atmosphere to form a c-axis-oriented Nd123 film.