Formation mechanism of defects around the Y211 inclusion trapped within the melt-textured Y123 domain

The melt processed Y123 oxide superconductor shows a very high magnetic levitation force and there is lots of research to develop its application technology such as a fly wheel energy storage device. Our recent study on the microstructure of the melt-processed samples showed that oxygenation condition significantly affected the magnetic properties of the YBCO sample. We examined the microstructure around the Y211 inclusion trapped within the melt-textured domain to understand the formation mechanism of the defects such as CuO stacking faults, dislocations and BaCuO platelet boundaries. The microstructures of the YBCO samples were heat-treated in flowing oxygen for various times. No defects were observed around the trapped Y211 inclusions and in the Y123 matrix of the tetragonal sample. Meanwhile, dislocation, transformation twins, the CuO stacking fault and BaCuO platelet structure were observed in the sample transformed into superconducting orthorhombic phase by low temperature heat treatment. The CuO stacking fault and BaCuO platelet structure are developed along the [100] and [010] direction on the a-b plane of the orthorhombic Y123. The formation mechanism of the defects was discussed on the basis of the oxygenation-induced decomposition mechanism.