STRUCTURAL ASPECT OF YBA2CU3O7-X FILMS ON SI WITH COMPLEX BARRIER LAYERS

The microstructure of YBa2Cu3O7-x (YBCO) thin films grown on Si with double (Y-stabilized ZrO2 (YSZ) and CeO2) or triple (MgO/CeO2/YSZ) buffer layers was characterized by means of transmission electron microscopy. The tetragonal distortion of the YSZ layer and the interaction between the MgO and CeO2 layers which lead to the formation of the MgCeO3 compound were found. The dislocation structure of the CeO2/YSZ interface consists mostly of 90 degrees dislocations with a presence of 60 degrees dislocation in the areas near the antiphase boundaries in YSZ. The YBCO films in both cases were oriented with the c-axis perpendicular to the substrate surface with a small density of a-axis oriented grains, The stacking sequence in the YBCO/CeO2 interface is mostly CeO2-BaO-CuO-BaO-CuO2-Y.... The presence of double CuO layers and other defects, due to atomic-height steps on the CeO2 surface, was observed, The YBCO films on the CeO2/YSZ buffer were single crystalline and those on the MgO/CeO2/YSZ buffer were polycrystalline with low- and high-angle grain boundaries between the grains. Small yttria precipitates in two epitaxial orientations were observed in the YBCO films.