Structure and formation mechanism of subgrains in large single-grain RE-Ba-Cu-O (RE = Y, Sm, Nd) bulk superconductors

We have studied the subgrain structures in large single-grain RE-Ba-Cu-O (RE = Y, Nd, Sm) bulk superconductors with polarized optical microscopic observations and micro-area X-ray pole figure measurements. Subgrains were formed in the early stage of grain growth, and were elongated along the growth direction with increasing their misalignment. Based on the comparative study of misorientation angles with the geometry of the second-phase particles, as well as microstructural defect studies using transmission electron microscope, the subgrains are created by the particle incorporation and their related lattice defects through the instability at the solidification front.