Effects of the initial heat-treatment conditions on microstructures of YbBa₂Cu₃O_7-δ superconducting final films deposited on SrTiO₃(001) substrates by the dipping-pyrolysis process

We investigated by transmission electron microscopy the relationship between the initial heat-treatment conditions and the microstructures of YbBa₂Cu₃O_7-δ superconducting final films deposited by a dipping-pyrolysis process on SrTiO₃(001) single crystal substrates. An amorphous precursor film was prepared by heating rapidly up to 425°C. By heat-treating at 725C, this film became a c-axis oriented YbBa₂Cu₃O_7-δ film with a thickness of 100 nm, and showed a sharp resistive transition around the critical temperature (T_c). On the other hand, a polycrystalline precursor film was produced by heating slowly. This film did not give rise to an epitaxial film, but to a YbBa₂Cu₃O_7-δ polycrystalline film with a grain size of about 200 nm, and exhibited a broad transition. Therefore, the initial heat-treatment conditions and the microstructures of the precursor films arc important for the epitaxial growth and superconducting properties of the final YbBa₂Cu₃O_7-δ films.