THE INFLUENCE OF BI DOPING ON THE IN-SITU GROWTH OF TLBA2CA2CU3O9 HIGH-T-C FILMS

The in situ process-laser ablation in combination with thermal evapora tion of Tl2O-has turned out to be a preparation method for single-phas e and epitaxial TlBa2Ca2Cu3O9 (1223) thin films with T-c values up to 109 K. It was found by several groups that a partial substitution of T 1 by Bi simplifies the phase development of the 1223 compound in the u sual two-step process. We have investigated the influence of the Bi do ping on the in situ growth. Xray measurements show that the films cons isted mainly of the 1223 compound. In 300-nm thin films there was no e vidence of a Bi amount in the crystal structure, but thinner films (80 nm) show a small amount of Bi. We concluded that Bi doping supports t he phase develop ment of the 1223 compound only in an early stage of t he film growth. The Bi-doped films have higher T-c values up to 114 K, higher j(c) values up to 6 x 10(5) A/cm(2) (77 K, 0 T), and lower sur face resistances of 56 m Omega (77 K, 87 GHz) than the undoped films.