PHASE-TRANSFORMATION DURING LOW-TEMPERATURE TL-DIFFUSION IN THE FABRICATION OF TL-BA-CA-CU-O THIN-FILMS

In the two-step fabrication of Tl-Ba-Ca-Cu-O thin films, Tl2Ba2Ca2Cu3O 10 (Tl-2223) and Tl1Ba2Ca2Cu3O9 (Tl-1223) films with good superconduct ing properties can be produced at a relatively low Tl-diffusion temper ature. Our study shows that although a low annealing temperature gener ally favors the formation Of Tl2Ba2Ca1Cu2O7 (n-2212) superconducting f ilm, Tl-2223 and Tl-1223 phases can still form by prolonging the annea ling time. In fact, a prolonged annealing time leads to the transforma tion from Tl-2212 phase to Tl-2223 phase, and then to Tl-1223 phase. T herefore, the annealing time must be carefully controlled to get the n eeded superconducting phase.