Platinum enhanced textured growth of grain-aligned YBa₂Cu ₃O_7-x thick films

The effects of magnetic alignment, heat treatment, and substrate interactions on the microstructural development and properties of YBa ₂Cu₃O_7-x (Y123) thick films were studied. Aligned films were formed by vacuum filtrating a particulate suspension in a 7 T applied field. These films and nonaligned control films were fired on either platinum (Pt) foil or magnesium oxide (MgO) substrates to various maximum temperatures between 930 and 1040°C. Optical microscopy revealed large differences in microstructural development between the various films. Aligned Y123 films fired on Pt foil exhibited the best microstructural properties. Via plasma emission spectroscopy and secondary ion mass spectroscopy, approximately 0.1 wt % Pt was found distributed throughout the films fired on platinum, while negligible amounts of Mg were detected in the films fired on MgO substrates. Differential thermal analysis revealed that, in the presence of Pt, the peritectic temperature (1030°C for pure Y123 in O₂) is reduced 70°C, thereby opening a substantial thermal processing window for partial melt assisted growth of textured Y123. SQUID measurements of magnetic hysteresis and T_c provided quantitative evidence that, relative to the films fired on MgO, those fired on Pt exhibited enhanced texture development [ΔM(H_app∥c axis)/ΔM(H_app⊥c axis)=2.6 at 5 K, 1 T] and properties (Bean model J_c,m=5×10⁴ A/cm² at 5 K, 4 T) without degradation of the T_c characteristics.