Reproducible synthesis by metal-organic chemical vapour deposition and thallium vapour diffusion of oriented thin-films Tl1+xBa2Ca2Cu3O9+x: intergrowth of Tl2Ba2Ca2Cu3O9 and Tl2Ba2Ca2Cu3O10 structures

Superconducting thin-films containing randomly disordered layers of Tl2Ba2Ca2Cu3O10 and Tl2Ba2Ca2Cu3O10 have been synthesized through a combined approach of metal-organic chemical vapour deposition (MOCVD) and thallium vapour diffusion. The BaCaCu matrices have been deposited onto yttria stabilized zirconia (YSZ) substrates using the second generation Ba(hfa)2 tetraglyme and Ca(hfa)2 tetraglyme (hfa denotes hexafluoroacetylacetonate), and the Cu(acac)2 (acac denotes acetylacetonate) as volatile metal-organic precursors. BaCaCu precursor films of composition 2:2:3 were annealed in the presence of a mixture of thallium (III), barium, calcium and copper oxides at temperatures of 840-860 deg. C and oxygen partial pressure varying from 0.04-0.5 atm. The formation of an oriented Tl1+xBa2Ca2Cu3O9+x (x approx. 0.5) intergrowth structure has been observed in narrow temperature and oxygen partial pressure ranges. The electrical resistivity data show Tc0=101 K which, in accordance with the scanning electron microscopy image, appears indicative of a material with weakly linked grains. (author)