Grain boundary properties of TlBa2Ca2Cu3Oxand Tl2Ba2CaCu2Oxthin films

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Abstract
We have investigated the transport properties of the grain boundaries of TlBa2Ca2Cu3Ox (Tl-1223) and Tl2Ba2CaCu2Ox (Tl-2212) epitaxial thin films. Both Tl-1223 and Tl-2212 thin films were grown on SrTiO3 bicrystal substrates with various tilt angles (5 degrees , 10 degrees , 15 degrees , 24 degrees and 36.8 degrees ) of (001) direction by a laser ablation and post-annealing method. For both Tl-1223 and Tl-2212 phases, the grain boundary Jc for large tilt angles ( theta >or=15 degrees ) at 5 K dropped by almost one order of magnitude, compared with the intragrain Jc. We also observed hysteretic magnetic-field dependence of grain boundary Jc for large tilt angles in both phases. On the other hand, the grain boundaries for low tilt angles ( theta c in low magnetic fields. The critical tilt angle was found to have the same value (10 degrees ) in both phases and greater than that ( theta approximately=5 degrees ) for the YBa2Cu3O7- delta system. These results suggest that the grain boundaries for high tilt angle larger than 15 degrees limit transport critical current density as weak links for Tl-Ba-Ca-Cu-O systems.