Polytypoidic superlattices in Y-Ba-Cu-O thin films

We report, for the first time, the observation of natural, polytypoidic superlattice structures in pulsed laser deposited superconducting Y-Ba-Cu-O thin films. These structures correspond to ordered stacking sequences of the "123", "124" and "224" cationic ratios. Such structurally coherent, natural superlattice structures, either in the stable or metastable form, may be an attractive alternative for the artificial superlattices suggested for novel electronic applications. The results suggest the existence of a family of polytypoidic phases with different cationic compositions in the Y-Ba-Cu-O phase diagram. © 1990.