NANOSTRUCTURAL CHARACTERIZATION OF INTERFACES OF THIN-FILMS OF YBA2CU3O7 WITH VARIOUS KINDS OF SUBSTRATES

The interfaces between thin film of YBa2Cu3O7 and various kinds of substrates were studied by high resolution electron microscopy. In the case of SrTiO3 as substrate, the interface contains no other phases and atomic stacking sequence was found to be: bulk(SrTiO3)-SrO-TiO2-BaO-CuO2-Y-CuO2-BaO-CuO-bulk(YBCO). Misfit dislocations in the YBa2Cu3O7 film were mostly found to extend only up to first few unit cells of YBa2Cu3O7. With MgO as substrate the first YBCO layer is the CuO layer, regardless whether the grain boundary is clean or contains a thin amorphous layer. In case of a clean grain boundary some strain occurs near the grain boundary, in particular in the MgO lattice. The interface of a YSZ substrate contains almost always an extra phase, which is probably BaZrO3. The first YBCO layer is also in this case a CuO layer. On the substrate NdGaO3 also a extra phase can occur, which is closely related to YBa2Cu3O7. This phase misses two layers of the YBa2Cu3O7 structure, resulting in a composition YBaCu2O5. The strain observed in the YBCO layer appears to decrease along the series SrTiO3-NdGaO3-YSZ-MgO.