Transmission electron microscopic studies on growth mechanism of YBa2Cu3O7−y films formed by advanced trifluoroacetates metalorganic deposition process

Abstract

Microstructure evolution of YBa2Cu3O7−y (YBCO) films during the two heat-treatments in the advanced trifluoroacetates metalorganic deposition (TFA-MOD) process has been investigated by means of transmission electron microscopy. In the calcination process, precursor films including nanopores were formed through the shrinkage of the film after a remarkable increase of the thickness due to the thermal decomposition of metalorganic salts in the starting solution. During the crystallization process, the densification and shrinkage of the film occurred after agglomeration of nanopores and coarsening of unreacted phase particles such as Y2Cu2O5, CuO, and Ba–O–F in the precursor films. The YBCO films were then epitaxially grown with the remaining unreacted phase particles in the film, finally pores were generated again by a reaction of these unreacted particles to form YBCO accompanied by the volume reduction. It is important to control the densification of precursor films and coarsening of the unreacted phase particles in the crystallization process, to fabricate YBCO final films with fine crystallinity and high critical current values.