ION-BEAM ANALYSIS OF HTC SUPERCONDUCTING TL-BASED FILMS

The elemental composition, film thickness and concentration depth prof iles of superconducting Tl-Ba-Ca-Cu-O and precursor Ba-Ca-Cu-O thin fi lms were studied by IBA techniques such as RES and NRA. The precursor Ba-Ca-Cu-O films were prepared by deposition of an aerosol (spray pyro lysis) atomized from aqueous nitrate solutions by ultrasonic excitatio ns. The substrates were single crystal MgO and yttrium-stabilized zirc onia (YSZ). The precursor Ba-Ca-Cu-O films were thallinated in a singl e-zone reaction chamber to produce the superconductor. The critical te mperature values, T-c, of the superconducting films ranged from 101 to 103 K and were found to consist of more than 95 vol.% of the Tl2Ba2Ca Cu2Ox phase. IBA studies revealed that the superconducting films were well oxygenated but slightly thallium deficient, with the Tl depth pro file decreasing from the bulk of the film to the surface. The phase co mposition was found to be different from the elemental one determined by IBA techniques, Moreover, residual carbon was found in both the sup erconducting and precursor films, Thermogravimetric studies revealed t hat it is highly probable that the carbon contamination was caused by exposure of the precursor oxide films to the ambient atmosphere prior to the thallination procedure. In regard to the optimization of the th allium content, the most important parameters of the dynamical thallin ation process were found to be the initial amount of Tl, the partial p ressures pTl(2)O and pO(2), the time of thallination and the reaction rate.