CRITICAL-CURRENT AS A FUNCTION OF FILM THICKNESS FOR SPRAY PYROLYZED FILMS OF TLBA2CA2CU3OY

It is imperative for tape applications to produce thicker films of TlBa2Ca2Cu3Oy with high critical current density on polycrystalline substrates (a useful figure of merit is the critical current per unit width, with a reasonable goal being 10 A mm(-1)). We have studied the critical current density at 77 K, 0 T (J(c)) as a function of film thickness in the range 2 to 10 mu m. A key parameter for obtaining a high J(c) was found to be the film density; firms with relative density > 82% showed much higher values of J(c). Based on average values, J(c) was found to peak at 60 kA cm(-2) for samples 2.5 to 5 mu m thick (corresponding to 3 A mm(-1) for 5 mu m thick samples), and to decrease for thicker samples, yielding 3 to 3.5 A mm(-1) from 5 to 10 mu m There are individual segments with values as high as 8.4 A mm(-1).