SIMPLE-MODEL FOR THE NUCLEATION OF (001)-ORIENTED AND (100)-ORIENTED GRAINS IN YBCO FILMS

A thermodynamical model, set up to describe the nucleation of vapour-d eposited YBCO thin films, is reported. The role of the surface energy of YBCO nuclei is discussed. Information on the surface Gibbs energy o f YBCO (100), (010) and (001) surfaces is obtained both from experimen tal results reported in the literature and from ab initio calculations . These data allow us to estimate the surface energy of the nuclei and to achieve a qualitative description of the crossover from (001) to ( 100) orientation at increasing supersaturation.