Melt-processing of YBa/sub 2/Cu/sub 3/O/sub x/ and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/: influence of processing parameters on microstructure and magnetization behavior

An investigation of the flux-pinning behavior of melt-processed YBa/sub 2/Cu/sub 3/O/sub x/ and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ has been carried out by means of microstructural investigations and magnetization measurements. It was found that both microstructure and magnetization behavior strongly depend on the chemistry and the grain size of the starting material. The carbon content and the melting behavior of the YBa/sub 2/Cu/sub 3/O/sub x/ powders seem to play an important role in the development of microstructure and flux-pinning behavior during melt-texturing. Carbon, which is existing in different amounts in all commercially available YBa/sub 2/Cu/sub 3/O/sub x/ powders and is also easily introduced during processing, was found to have the same detrimental influence on the grain boundaries of melt-processed materials as on the grain boundaries of sintered pellets. On the other hand an increase in the flux-pinning behavior could be found when carbon was present during the melting and resolidification process. Our results indicate that the presence of carbon during the resolidification process results in the incorporation of precipitates and defects not only into the grain boundaries, but also into the bulk of YBa/sub 2/Cu/sub 3/O/sub x/ leading to an increased intragrain critical current density. Initial experiments indicate that a similar effect might also be possible for Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/.<>