Preparation and physical properties of superconducting films in the Tl–Ba–Ca–Cu–Agx–O system prepared by spray pyrolysis and Tl-diffusion

Superconducting films of Ag-doped Tl–Ba–Ca–Cu–O with a varying molar ratio of Ag dopant ranging from 0 to 0.5 were prepared by spray pyrolysis of Ba–Ca–Cu–Ag–O precursor films on MgO substrate, and then post annealed with Tl-bulk sources. Phase transformation of the multiple phases of Tl-2212 and Tl-1223 to a single-phase of Tl-2223 was observed in the Ag-doped Tl–Ba–Ca–Cu–O superconducting films annealed at temperatures close to the melting point, 885 °C. The critical transition temperature (Tc,R=0) increased and electrical resistivity decreased as the dopant concentration increased up to 0.5. Doping effect of Ag in the Tl-based film not only improves the critical transition temperature and current density but also facilitates the formation of single-phase Tl-2223 at lower temperature. Critical transition temperature (Tc,zero) and current density (Jc, 77 K, 0 T) of the best resultant Tl-based film were shown to be 123 K and 5.7 × 104 A/cm2, respectively.