Competition between a-axis and c-axis growth in superconducting $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ thin films

The competition between a-axis and c-axis growth in $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ $(R=\mathrm{r}\mathrm{a}\mathrm{r}\mathrm{e}-\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{t}\mathrm{h}$ or Y) superconducting thin films has been analyzed. Stoichiometric and Nd-rich NdBaCuO thin films have been deposited by dc 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 $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ oxides, is obtained as a 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 $a/c$-axis content of other $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ oxides.