Effect of $\hbox {Y}_{2}\hbox {O}_{3}$ Seed Layer on Epitaxial Growth of Oxide Barrier Layer for YBCO Coated Conductor

Y₂O₃ film was deposited as the seed layer by dc reactive sputtering technique on a Ni-5at%W (NiW) substrate. The subsequent oxide buffer layers were introduced as well such as Gd₂Zr₂O₇ (GZO) and La₂Zr₂O₇ (LZO). The effects of Y₂O₃ seed layer on the epitaxial growth of buffer layers and the performance of YBa₂Cu₃O_7-δ (YBCO) films were investigated. The atomic force microscopy images showed that the surfaces of Y₂O₃ seed layers were homogeneous and flat with the root mean square roughness of about 1.2 nm, which is significant for the subsequent layers. In contrast, root mean square roughness values of GZO films on bare NiW or Y₂O₃ seeded NiW were normally about 2.7-3.4 nm. A series of X-ray studies indicated that the GZO and LZO oxide barrier layers on Y₂O₃ can be epitaxially grown easily with a wide processing condition of water vapor partial pressure. Furthermore, the effect of Y₂O₃ seed layer on subsequent YBCO films was investigated by comparing the transition temperature Tc and the critical current density .Ic between YBCO/GZO/NiW and YBCO/GZO/Y₂O₃/NiW. These results demonstrate the notable role of the Y₂O₃ seed layer, not only on high-efficiency production of subsequent functional, but also on the improvement of superconducting performances of YBCO films.