Recently, considerable efforts have been made in growing bi-axially aligned thick Yba2cu3O7 (YBCO) films on a flexible, textured metallic substrate for electrical power applications. The BaF2 post-deposition annealing process is one of the most promising methods. to understand the nucleation and growth mechanism of YBCO in this process, extended transmission electron microscopy analysis has been made. Here, we report on the evolution of Ba-Y oxy-fluoride which is pertinent to the epitaxial YBCO nucleation process on SrTiO3 (STO) substrate.
The stoichiometric ratio of Y, Cu and BaF2 was evaporated on (00l)-cut STO substrate Subsequently, these films were annealed at 735°C in an O2-H2O-N2 gas atmosphere and quenched after 10, 20, or 40 minutes. The morphology and phase composition of the precursor changed drastically with the annealing times, e.g. after 10 minutes heat treatment, the precursor consisted of fine grained CU2O and Ba-Y(Cu) oxy-fluoride (cubic, a=0.618nm) as shown in fig.la.