THE INTERFACIAL ATOMIC-STRUCTURE OF EPITAXIAL YBCO THIN-FILMS ON Y2O3

The detailed atomic structures at the interfaces of laser-ablated epit axial YBa2Cu3O7-x (YBCO) thin films on Y2O3 were characterized by high -resolution electron microscopy and multi-slice image simulations. Two cases of stacking sequences were found at the YBCO/Y2O3 interfaces. I n the first case, the first atomic layer of the YBCO at the interface is a BaO plane, with the Ba atoms positioned 0.3 nm (projected distanc e) above the upper Y plane of the Y2O3. In the second case, a CuO2-lik e plane is the first atomic layer of the YBCO film, with the Cu atoms positioned 0.2 nm (projected distance) above the upper Y plane of the Y2O3. The images are insensitive to the oxygen arrangement at the inte rfaces. Close to the interface, (001) stacking faults are found in som e cases, involving extra CuO and heavy-cation (Y or Ba) planes, before the perfect stacking of YBCO is established further away from the int erface.