Subgrain structures and superconductivity in RE-Ba-Cu-O bulk superconductors

We have studied the microstructures of subgrains in large single-domain RE-Ba-Cu-O (RE=Y, Nd, Sm) bulk superconductors through microscopic observation and microarea X-ray pole figure analyses. The misorientation angle of subgrains increases as the crystal growth proceeds, and thus more crystal defects such as dislocations are seen at the later stage of the growth. Electron backscatter diffraction technique was successfully utilized for characterizing the subgrain boundaries. Electric and magnetic measurements for several samples containing different subgrain geometries have been performed. The results of I-V and resistivity measurements indicated that subgrains act as weak-links especially in a high magnetic field region.