MAGNETIC-FLUX PINNING PROPERTIES OF OXIDE SUPERCONDUCTORS PRODUCED BY MELT PROCESSES

The flux pinning mechanism of YBaCuO superconductors produced using a melt process was investigated by measuring the magnetic field dependence of transport critical current densities (Jc) at 77 K. Superconductors produced by the melt process had high transport Jc values and the magnetic field dependence of the transport Jc was quite small compared to that of bulk sintered materials. This suggests that, in this case, Jc in a high field region is determined by flux pinning within the bulk of the material. Using procedures based on conventional flux pinning theory, the Jc-B properties were analysed to estimate dominant pinning sites in solidified specimens. According to the theoretical analysis and microstructural observations, the expected site of dominant pinning is the normal precipitates dispersed in the YBaCuO grains, and the transport Jc may be determined by their average size and density. © 1990.