Formation of superconducting (Tl,Bi)Sr2CaCu2Oy thin films by rf sputtering and thallium diffusion

We have prepared new high Tc superconducting thin films of (Tl,Bi)-Sr-Ca-Cu-O by combining low temperature (500 °C) rf sputtering of Bi-Sr-Ca-Cu-O precursor films and thallium diffusion. A typical film has Tc(onset) =80 K, Tc(midpoint) =79 K, and Tc(zero) =50 K. X-ray diffraction and energy dispersive spectroscopic studies were carried out to determine the composition and crystal structure of the superconducting phase within the film. We identified a material with the chemical composition of (Tl0.7 Bi0.3 )Sr2CaCu2Oy and tetragonal symmetry (a=3.795 Å and c=12.095 Å), and propose that this phase is responsible for superconductivity around 80 K. The film also has a highly preferred orientation with the c axis perpendicular to the surface of the (100)MgO substrate.