INFLUENCE OF DIFFERENT MELT PROCESSINGS UPON THE MICROSTRUCTURE AND CRITICAL-CURRENT OF TEXTURED Y123

Since directional solidification has been shown to be a successful way for achieving high critical current densities in bulk YBCO, many diff erent ways have been developed for the sample preparation. In this stu dy, the microstructure and superconducting properties of several proce ssing routes (melt powder melt growth, powder melt processing, solid l iquid melt growth) have been comparatively investigated. These process ings are distinguished essentially from the combination of different s tarting precursors. It is shown that Y2BaCuO5 (Y211) excess in the nom inal composition and/or 0.5 wt.% platinum doping strongly influence th e shape of the Y211 formed during the high temperature melting stage o f the texturing process. Spherical or thin needle-shaped Y211 grains c an be obtained and their size controlled. Microstructural correlations have shown that the nucleation and growth mechanisms of Y211 grains d etermine the further YBa2Cu3O7-delta (Y123) formation. Thus, MPMG and SLMG processes appear to be governed by the diffusion of yttrium and a lso the dissolution mechanism of acicular Y211, while PMP process is m ainly controlled by the diffusion of yttrium in the liquid phase to th e Y123 growth front. However, the best Bean critical current densities between 0 and 1 T are obtained for the MPMG samples, but with improve d processing conditions, the PMP process might be promising.