We have studied the structure of subgrains in large-grain RE123 (RE = Y, Sm) bulk superconductors, and their influences on superconducting properties. It was found from polarized optical microscopic observations that subgrains were formed in the early stage of grain growth and elongated along the growth direction with increasing their misorientation angles. For isothermally grown samples, subgrains are likely to form under large undercooling. Based on a comparative study of misorientation angles calculated through micro-area x-ray pole figure measurements with the geometry of the second-phase particles, the possible mechanism of subgrain formation was concluded to be the accumulation of dislocations formed as a result of entrapment of RE211 inclusions during crystal growth.
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