Effects of Synthesis Conditions on Microstructure of a YBa2Cu3Ox Superconductor by Partial Melting Process

The synthesis conditions of a partial melting process for a bulk YBa2Cu3Ox (123) superconductor are discussed in terms of the microstructure and superconducting properties. The overall process consists of the partial melting, in which Y2BaCuO5 (211) and a liquid phase form, and subsequent slow cooling for the formation of the 123 grains by a peritectic reaction of 211 with liquid. Melt-quenched and sintered starting materials were examined to understand the difference in microstructural development. During partial melting, the grain size of 211 was considerably dependent on the starting materials. Melt-quench-derived materials produced much finer 211 than sinter-derived materials. After the peritectic reaction, the residual 211 inclusions were trapped inside the 123 grains. The size of the 211 inclusions was almost equivalent to that during the partial melting. The 123 grains also included defects such as cracks and streaks which may have formed due to inhomogeneities in the peritectic reaction during the growth of the 123 grains. The melt-quench-derived materials included fewer defects than the sinter-derived materials. The finely and homogeneously dispersed 211 grains present in melt-quench-derived samples are considered to be effective in reducing defects by promoting a smooth and uniform peritectic reaction. As a result, melt-quench-derived materials showed better critical current densities than sinter-derived materials.