Transmission electron microscopic studies of YbBa₂Cu₃O_7-δ superconducting final films formed on LaAlO₃(001) substrates by the dipping-pyrolysis process

We investigated the relationship between final heat-treatment conditions and microstructures of YbBa₂Cu₃O_7-δ films formed on LaAlO₃(001) substrates by the dipping-pyrolysis process. First, we spin-coated the substrates with a solution including metal organic compounds. Second, we heated them at 425°C in air to form amorphous precursor films. Finally, YbBa₂Cu₃O_7-δ films were prepared by the final heat-treatment of the precursor films at 750°C in an Ar gas flow under various conditions of heating rate and holding time. The microstructures of these final films were studied by transmission electron microscopy. It has been found that a rapid heating rate is necessary for the epitaxial growth of the superconducting films, and that a long holding time is effective for the grain growth of the crystals. The transmission electron microscopic studies revealed different microstructures of the final films, although X-ray diffraction patterns did not distinguish them.