FABRICATION OF TBCCO FILMS VIA SEQUENTIAL ELECTRODEPOSITION AND CO-ELECTRODEPOSITION OF THALLIUM-FREE PRECURSORS

Tl-Ba-Ca-Cu-O (TBCCO) superconducting films have been prepared via the incorporation of Tl vapour into co-electrodeposited and sequentially electrodeposited Ba-Ca-Cu-O (BCCO) precursors on ceramic substrates and silver foils. The BCCO films were electrodeposited at a constant potential of -3 to -5 V (versus Hg/Hg2SO4, [SO42-] = 1 M) from a single electrolyte or multiple electrolytes. The results suggest that the Bcco precursors deposited by the novel hybrid sequential electrodeposition provide a better stoichiometry control than those deposited by co-electrodeposition due to the great difference (> 0.2 V) in standard reduction potentials among the cation species (Ba2+/-2.906 V, Ca2+/-2.866 V, Cu2+/0.337 V versus SHE). Superconducting films with reliable properties have been prepared on polycrystalline zirconia plates and rods. These films contain multiple superconducting phases with a plate-like morphology and have transition temperatures in the range 95-105 K. The best film on MgO(100) has a thickness of < 5 mum and shows a T(c) (R = 0) at 111 K and J(c) > 2 x 10(3) A cm-2 at 77 K. The best film on silver foil shows a promising J(c) > 103 A cm-2 at 77 K.