Crystallization mechanism of Nd_(1+x)Ba_(2-x)Cu_3O_(7-y) and YBa_2Cu_3O_(7-y) films deposited by metalorganic deposition method using trifluoroacetates

摘要

YBa_2Cu_3O_(7-y) (Y123) and Nd_(1+x)Ba_(2-x)Cu_3O_(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 LaAlO_3 (001) and SrTiO_3 (STO) (001) substrates, respectively, with solutions including trifluoroacetates. Then, the samples were heat treated at 673 K in a humid O_2 gas flow to form amorphous precursor films. Finally, the precursor films were heated at higher temperatures for 0-30 min in a humid Ar/O_2 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 Y_2Cu_2O_5, BaF_2, and CuO crystals was found to be generated on the c-axis-oriented Y123 film. In contrast, in the Nd123 quenched films, (Nd,Ba)_2CuO_4(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 Y_2Cu_2O_5, BaF_2, and CuO crystals, and the Nd201 phase reacts with BaF_2 and CuO crystals in a humid atmosphere to form a c-axis-oriented Nd123 film.