Critical current density and microstructure of 7–8 μm thick spray pyrolyzed films of TlBa2Ca2Cu3Oy

Abstract Tape applications require high values of critical current density in thick films of TlBa 2 Ca 2 Cu 3 O y (Tl-1223). Previous work on polycrystalline YSZ substrates has shown average values of J c (77 K, 0 T) = 60 kA cm −2 for films 3–5 μm thick. The effect of varying the substrate temperature (853–868°C) during thallination in a two-zone flow-through furnace is studied here for thicker films (7–8 μm thick). Film density and the zero-resistance transition temperature increase with increasing processing temperature, as does the amount and size of the plate-like features on the film surface. X-ray diffraction shows that alignment improves with increasing temperature, but is still below values obtained for 3 μm thick films. Phases other than Tl-1223 were found at all processing temperatures. Values of J c for the 7–8 μm thick films are generally lower than for the thinner 3–5 μm thick ones, but the current per sample width can be higher (the highest value for the thinner films was 5 A mm −1 , whereas at substrate temperatures > 860°C, 7% of the segments of the 7–8gmm thick films had values A mm −1 .