The atomic structure at the (001) surface of GdBa2Cu3O7-δ obtained by cleavage of melt-textured material was determined with high resolution electron microscopy. It was observed that in a majority of the clean (001) surfaces, the surface layer was a CuO2 layer neighbouring the Gd-vacancy layer of the bulk (bulk-Gd-CuO2-vacuum). The preference for this termination at the CuO2 layer did not depend on δ. For this termination a √2 x √2 surface reconstruction occurred. For the second most occurring interruption: bulk-CuO1-δ-BaO-vacuum the surface relaxation was rather small. The surface reconstruction and surface relaxations could explain the absence of a superconducting energy gap in the photoemission spectra.

A √2 x √2 Surface Reconstruction of (001) Cleaved GdBa2Cu3O7-δ. H.W.Zandbergen: Physica C, 1992, 194[3-4], 287-92