Microstructure evolution of YBCO films deposited by advanced TFA-MOD process

We have investigated microstructure evolution of YBa₂Cu₃O_7-y (YBCO) films through the two steps of heat-treatments in the advanced TFA-MOD process, by means of transmission electron microscopy. In the calcination process, precursor films including nanopores are formed with shrinkage of the film after a remarkable increase of the thickness caused by gas generation due to thermal decomposition of metalorganic salts in the starting solution. During the crystallization process, the densification and shrinkage of the film occurs after agglomeration of nanopores and unreacted phase particles such as Y₂Cu₂O₅, CuO and Ba-O-F in the precursor films. Before starting of YBCO epitaxial growth, the densification and shrinkage of the film occurs. The YBCO films are epitaxially grown with remaining the unreacted phase particles in the film, subsequently pores are generated again by a reaction of these unreacted particles to form YBCO accompanying with the volume reduction. In conclusion, it is important to control the densification of precursor films and the coarsening of the unreacted phase particles in the crystallization process, in order to fabricate YBCO final films with fine crystallinity and high I_C values.