The Influence of Bi Doping on the In Situ Growth of TlBa2Ca2Cu3O9 High- Tc Films.

The in situ process—laser ablation in combination with thermal evaporation of Tl₂O—has turned out to be a preparation method for single-phase 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 Tl by Bi simplifies the phase development of the 1223 compound in the usual two-step process. We have investigated the influence of the Bi doping on the in situ growth. X-ray measurements show that the films consisted mainly of the 1223 compound. In 300-nm thin films there was no evidence 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 the phase development of the 1223 compound only in an early stage of the film growth. The Bi-doped films have higher T_c values up to 114 K, higher j_c values up to 6 × 10⁵ A/cm² (77 K, 0 T), and lower surface resistances of 56 mΩ (77 K, 87 GHz) than the undoped films. [ABSTRACT FROM AUTHOR]