Transport critical current densities in bulk Tl2Ba2 Ca2Cu3Ox and polycrystalline-thin-film Tl2Ba2Ca1Cu 2Ox: dependence on microstructure and neut

The authors report investigations of the dependence of transport critical current density, J_c, upon magnetic field, B, at 4, 64, and 75 K in a bulk ceramic sample of Tl₂Ba₂ Ca₂Cu₃O_x and in a polycrystalline, textured thin film of Tl₂Ba₂CaCu ₂O_x. In ceramic samples of Tl-2223, the authors generally observe the double-step J_c versus B characteristic, in which J_c drops from its zero field value to a plateau reached at B~100 Oe. The plateau region then extends to a higher field B*(T) beyond which J_c(B) decreases monotonically. Plateau J_c (75 K, 1.0 T) values>300 A/cm² with B*(75 K)~1.5 T were achieved. In these samples, a pronounced peak effect is observed in which J _c(B) increases monotonically with increasing B for 100<B(O _e)<B*. After neutron irradiation, B* is observed to be significantly enhanced, suggesting that B* signals the onset of rapid flux creep. The textured polycrystalline film shows enhanced values of J_c~2×10⁵ A/cm² at 64 K, O T and the absence of weak-link behavior