Tl-based superconducting films by spray pyrolysis and MOCVD

Tl-1223 and Tl-2223 superconducting films have been prepared using spray pyrolysis and MOCVD for the deposition of the precursor layer and a solid source of thallium for the subsequent thallination step. For the former phase, critical temperatures and critical current densities up to 113 K and 2.5 MA/cm2 (77 K, 0 T) have been obtained after 3 to 6 hours at 860-870°C. Pure Tl-2223 films are by far more difficult to prepare. This can be achieved by operating at 890-900°C or with a fluorine containing source. The resulting films have then poor superconducting properties due to the presence of holes. Working at 875°C yields multiphase films (Tl-2223 + Tl-2212 or Tl-2223 + Tl-1223) with however better properties