TLBACACUO SUPERCONDUCTING THIN-FILMS VIA METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION (MOCVD) AND THALLIUM VAPOR DIFFUSION

Superconducting thin films of the TlBaCaCuO family have been prepared through a combined approach of MOCVD and thallium vapour diffusion. A three-step process has been adopted involving i) the synthesis of Ba-Ca-Cu-O films by MOCVD using <<second-generation>> barium and calcium sources, ii) the hydrolysis of the fluoride phases by annealing in water vapour-saturated oxygen and iii) the annealing in the presence of a thallium source. Reproducible results, in terms of phase formation, are discussed depending on the different conditions of the preannealing process. The superconducting films consist predominantly of single-phase Tl2Ba2Ca2Cu3Ox(2223). Preferential orientation of the crystallite c-axes perpendicular to the substrate surface has been observed. The films exhibit superconducting onset temperatures of 115-120 K with zero resistance higher than 100 K.