a1 Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
Magnetron sputtering was used to deposit superconducting YBCO thin films on four polycrystalline metal substrates. Yttrium-stabilized zirconia (YSZ) and silver were used as buffer layers. The thermal expansion coefficient of the substrate was apparently correlated to the properties of the superconductor. Auger depth profiles showed that the YSZ buffer blocked diffusion of most metal elements from the substrate. Nevertheless, contamination of the films depressed Tc to 81 K on Hastelloy × from 87 K on single-crystal strontium titanate. The films on metal substrates were c-axis oriented, but with random rotation in the a-b plane and smaller grain size than epitaxial films on single crystals. The weak links from these factors restrict Jc to 104 A/cm2 at 40 K.
(Received December 23 1991)
(Accepted March 24 1992)