Scanning and transmission electron microscopy studies of the interface between the Tl-1223 phase and yttria doped zirconia substrates

High purity (Tl0.5Pb0.5)(Ba0.2Sr0.8)2Ca2Cu3Ox superconducting 20 – 60 µm thick films with Tc(0)-values of between 110 and 115 K and transition widths of 2 to 4 K were fabricated on polycrystalline 9 mol-% Y2O3-doped ZrO2 (YSZ) substrates by the screen-printing. The microstructure and the phase composition at the interface of the superconducting Tl-1223 film and the substrate were analyzed by transmission electron microscopy, scanning electron microscopy, and selected area electron diffraction and by energy dispersive X-ray fluorescence analysis. The interface between the substrate and the superconducting film consisted of several phases formed by the reaction between the thallium superconductor and zirconium dioxide. Analyses of the substrate/film interface performed by energy dispersive X-ray fluorescence showed the presence of a Ba-(Pb-Sr)-Zr-O compound close to the substrate. This phase was responsible for the very good adhesion of the superconducting films to YSZ substrates. Additional phases found at the interface were CaO, calcium strontium cuprates and barium cuprate.