Tl₁Ba₂Ca₂Cu₃O_x系超電導薄膜の超電導特性

抄録

We have investigated a correlation between structure and superconducting properties ofTl₁Ba₂Ca₂Cu₃O_x [Tl-(1223)] thin films. The Tl-(1223) thin films were prepared on SrTiO₃, LaAlO₃ and MgO (100) substrates by Metalorganic deposition method. Films grown on SrTiO₃ and LaAlO₃ exhibit a particularly high degree of epitaxial growth, which may be attributed to the remarkably close lattice matching. Then, these films had high Jc>10₅A/cm₂ at 77K in a zero magnetic field. However, in case of MgO, the film was distributed randamly and had low Jc of about 10₃A/cm₂ at 77K in 0T. Moreover, in case of magnetic field applied perpendicular to the a-b plane, we found that the field transport properties of the Tl-(1223) thin films were superior to those of the Tl₁Ba₂Ca₂Cu₃O_x[Tl-(2223)] andBi₂Sr₂Ca₂Cu₃O_x[Bi-(2223)] thin films. On the other hand, grain boundary properties of the Tl-(1223) thin films depended on (001) tilt angles of grain boundaries. We found that low tilt angle (θ_??_10°) grain boundaries did not work as a weak link and retained high Jc However, it is well known that grain boundaries for (θ_??_5°) in Y₁Ba₂Cu₃O_x[Y-(123)] thin films are weak links. It suggests that the Tl-(1223) system is superior to Y-(123), Tl-(2223) and Bi-(2223) systems as a material for high field applications at high temperatures.