Nanostructural characterization of interfaces of thin films of YBa 2Cu 3O 7 with various kinds of substrates

Abstract

The interfaces between thin film of YBa 2Cu 3O 7 and various kinds of substrates were studied by high resolution electron microscopy. In the case of SrTiO 3 as substrate, the interface contains no other phases and atomic stacking sequence was found to be: bulk(SrTiO 3)-SrO-TiO 2-BaO-CuO 2-Y-CuO 2-BaO-CuO-bulk(YBCO). Misfit dislocations in the YBa 2Cu 3O 7 film were mostly found to extend only up to first few unit cells of YBa 2Cu 3O 7. 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 BaZrO 3. The first YBCO layer is also in this case a CuO layer. On the substrate NdGaO 3 also a extra phase can occur, which is closely related to YBa 2Cu 3O 7. This phase misses two layers of the YBa 2Cu 3O 7 structure, resulting in a composition YBaCu 2O 5. The strain observed in the YBCO layer appears to decrease along the series SrTiO 3-NdGaO 3-YSZ-MgO.