COMPOSITION AND PHASE DEVELOPMENT OF EPITAXIAL SUPERCONDUCTING TL0.78BI0.22SR1.6BA0.4CA2CU3O9-DELTA THIN-FILMS BY LASER-ABLATION AND POST ANNEALING

For the formation of epitaxial superconducting Tl0.78Bi0.22Sr1.6Ba0.4C a2Cu3O9-delta ((Tl,Bi)-1223) thin films, the dependence of phase devel opment on the chemical state of the source materials, deposition dista nce from source to substrate, and O-2 pressure during deposition by la ser ablation and post annealing was studied by X-ray diffraction (XRD) , scanning electron microscopy (SEM), and energy dispersive spectrosco py (EDS). It was found necessary to have thallium in the precursor fil m and that a reacted source target is better than the unreacted source for obtaining (Tl,Bi)-1223 phase-pure films. Better(Tl,Bi)-1223 films were obtained at a deposition distance of 44 mm from source to substr ate than at a distance of 61 mm over a range of O-2 pressure from 5.7 to 31.3 mTorr The best films prepared under the optimal conditions exh ibited transport J(c) close to 3 X 10(6) A/cm(2) at 77 K and zero fiel d.