Subgrain structures in RE123 bulk superconductors

We have studied the microstructures of subgrains in large-grain RE123 (RE = Y, Sm) bulk superconductors through microscopic observation and x-ray pole figure analyses. For the samples grown by slow-cooling, misorientation of the subgrains increases along with the crystal growth, and also that the misorientation has positive relation to the size and concentration of the second-phase particles. For isothermally grown samples, subgrains are likely to form under large undercooling. We discuss the possible mechanism of subgrain formation. Such subgrains are considered to affect current carrying capabilities in bulk materials, so that we performed magnetic and electric measurements for several samples having different subgrain structures. The results of J_c-B and AC transport measurements indicated that the subgrains act as weak-links, especially under high magnetic fields.