Fabrication of Ca-doped REBa2Cu4O8 films by the molten hydroxide method

In order to improve a critical current density (Jc) under applied magnetic fields, it is well known that the RE-Ba-Cu-O superconductors are required an improvement of a critical temperature (Tc). Although the Tc of REBa2Cu4O8 (RE124) is inferior to REBa2Cu3Oy (RE123), RE124 has rigorous stability of oxygen stoichiometry. Furthermore, the RE124 has an important advantage that the Tc was improved by Ca-doping. In this study, in order to improve Tc of RE124, we fabricated the Ca-doped RE124 (RECa124) films by using molten hydroxide method. The orientation of Y124 and YCa124 films showed a c-axis orientation completely and the Tc of YCa124 film showed 10 K higher than that of the Y124 film. However, GdCa124 and SmCa124 films contained RE123 phase by much compare with YCa124 films and the Tc were decreased with increasing of RE ionic radius over YCa124.