JOSEPHSON BEHAVIOR FOR HIGH CRITICAL CURRENT-DENSITY YBCO+AG THICK-FILMS ON YSZ SUBSTRATES

High critical current density thick films of yttrium barium copper oxide plus 10 wt.% silver have been fabricated on yttria stablised zirconia substrates. The films are approximately 10 μm thick, superconducting with Tc(R = 0) in the range 90.5 to 91.0 K and are found to have jc's close to 3000 A cm-2 at 77 K in zero applied magnetic field. The thermal cycle for the production of these films requires the use of temperatures in excess of the peritectic and therefore involves melt processing. This has a number of advantages, including film texturing, which is significantly improved with the addition of Ag, and the formation of an inert BaZrO3 barrier layer which has fine CuO needles dispersed throughout. This layer prevents atomic diffusion and film poisoning. At 77 K, the jc values decreased markedly for applied magnetic fields increasing from 0-20 Oe, and then decreased slowly for increasing fields, being almost constant for field values ∥#62; 150 Oe. The temperature variation, near Tc, of the critical current ic was best described by ic £ (1 - T/Tc)1.52, the Ginzburg-Landau 3 2 power law characteristic, and indicates that the granular films may be modelled as an array of Josephson-coupled grains which have a short coherence length. Variable thickness bridges patterned into the thick films showed very clear DC and AC characteristics that were very similar to those expected from a single Josephson junction. © 1990.