The microstructures of MTG YBCO near 211 phase clusters inside the sample have been studied by means of transmission electron microscope. The results indicate that crystal defects around 211 phase are closely related to the distance between 211 particles (d211).With the decease of d211, the twin spacing increases. Simultaneously, the thickness of twin boundary decreases. When d211 is less than 0.51μm, there are almost no defects between 211 particles. By establishing crack model, we have analyzed the mechanism of the emergence of defect-free-zone. The relationship between d211 and Jc has been discussed in this paper.
Chinese Journal of Low Temperature Physics