Influence of inhomogeneity on flux pinning for MTG YBCO bulk

Large cylindrical YBa2Cu3O7−y (YBCO) single grains with diameter of 25 mm are successfully fabricated. Three specimens cut from different parts of one grain are studied to probe the homogeneity of critical current density. Magnetic hysteresis loops show that flux pinning behaviors of the specimens are different for each other, which may be originated from different oxygen content and size of Y2BaCuO5 (Y-211) particle as observed by the critical temperature and morphology measurements. The results indicate that the YBCO bulk is not homogenous enough, and homogeneous oxygen vacancies as well as small Y-211 particles are necessary to obtain stronger flux pinning. In addition, we examine the fishtail effect (FE) and discuss the mechanism of FE in the specimens.