Microstructure near 2 1 1 phase in high Jc MTG YBCO

The microstructures of MTG YBCO near 2 1 1 phase clusters inside the sample are studied by means of transmission electron microscopy. The results indicate that crystal defects around 2 1 1 phase are closely related to the distance between 2 1 1 particles (d _{2 1 1}). With the decrease ofd _{2 1 1}, the twin spacing increases. Simultaneously, the thickness of the twin boundary decreases. Whend _{2 1 1} is less than 0.51 m, there are almost no defects between 2 1 1 particles. According to the established crack model, the mechanism of the appearance of a defect-free-zone is explained. The relationship betweend _{2 1 1} and Jc is discussed in this paper.