Competition between alpha-axis and c-axis growth in superconducting RBa2Cu3O7-x thin films

The competition between a-axis and c-axis growth in RBa2CU3O7-x (R = rare-earth or Y) superconducting thin films has been analyzed. Stoichiometric and Nd-rich NdBaCuO thin films have been deposited by de sputtering. The relative a/c-axis content has been estimated by x-ray diffraction and plotted as a function of deposition temperature. Comparison of obtained results with the experimental data available for other compounds yields clear evidence that a universal behavior, valid for RBa2Cu3O7-x oxides, is obtained asa function of a normalized deposition temperature. A model for the nucleation of supercritical clusters from a multielemental adsorbed phase, allowing us to face the problem of phase competition in complex compounds, is presented. As a particular case, the competition between different phases of a single compound is analyzed as a function of supersaturation. A general behavior for the orientation dependence as a function of a normalized deposition temperature is thus obtained. It is shown that our experimental results about the relative a/c-axis content fall on the theoretical curve. The same procedure is also successfully applied to all the data derived from the literature regarding the relative ale-axis content of other RBa2Cu3O7-x oxides.