Distribution of magnetic flux in high-Jc YBa2Cu3O7 superconductors

We present high-resolution Bitter patterns which reveal the flux distribution in high-J c melt-textured growth superconductor YBa 2 Cu 3 O 7 at 64K. Glass type of spatial configuration of vortex was observed and it supports the vortex glass model. In addition to the conventional pinning sites, such as twin boundaries, grain boundaries, microcracks etc., the dispersed small particles, ≤0.5μm in size, of the second phase also cause flux pinning. The strongest pinning appears in the vicinity of large grains of second phase, where the crystal lattice is seriously distorted.