Y2BACUO5 EXCESS AND QUENCHING INFLUENCES ON MELT-TEXTURED YBCO

We investigated the influence of the preliminary heat treatments of precursor oxides (calcination and/or quenching) and their stoichiometries (various amounts of Y2BaCuO5 (Y-211) phase excess) on the melt-textured growth Of YBCO samples. We tried to correlate the process parameters with the obtained microstructures and the exhibited superconducting properties at 77 K, i.e. magnetic interaction forces as a function of the distance from a permanent magnet and magnetization hysteresis at different applied magnetic fields. The results revealed the positive effects of Y-211 phase excess (20% molar) and of quench treatment of BaO2 + CuO precursor oxides. We found the importance of fine and homogeneous Y-211 residual particle distribution, which is favoured both by adding an excess of Y2O3 powder instead of Y-211 preprepared powder and by the introduction of a quench treatment before the growth process. We analysed materials produced with different quenching conditions of precursor powders in order to optimize the process. Magnetization critical current densities of 2.2 x 10(4) A cm-2 and 1.4 x 10(4) A cm-2 were evaluated at 77 K with 0.1 T and 1 T fields applied parallel to the sample c axis.