TRANSPORT-PROPERTIES AND SURFACE-MORPHOLOGY IN Y123 FILMS ON METALLICSUBSTRATES WITH GRAIN-ORIENTED BUFFER LAYER

It has emerged after many years of research that to obtain good-qualit y high-T(c) superconducting Y1Ba2Cu3O7-delta (referred to as Y123 here ) films on metallic (Hastelloy C-276) substrates, cubic yttria stabili zed zirconia (frequently referred to as YSZ) is an excellent buffer la yer. It was found that the use of a Pt underlayer, under this buffer l ayer, helps the further improvement of the transport behavior in such films. In order to elucidate the effect of such metallic underlayer co atings in detail, we have used various other metallic underlayer coati ngs, like Pd, Au, Ag in addition to the previously used Pt, in this re port. We show that the role of metallic underlayer coating is in impro ving the surface morphology. Thin layers (20 nm) of these metals with their noble properties act as a barrier for the interaction between th e substrate and the buffer layer, and thus finally improve the surface morphology. Detailed X-ray measurements reveal that the quality of th e films was directly linked to the percentage mismatch between the lat tice parameters of YSZ and Y123 film. Two distinctly different grain m orphologies are noticed. This difference is discussed in terms of the film quality.