Unusual Change in Columnar Defect Morphology in YBCO upon Annealing

摘要

We show evidence from transmission electron microscopy of an unusual change in columnar defect morphology in YBCO upon annealing to 600 deg C. The disappearance of the nanotwinned, but not the larger scaled thermal twinned, structure is found. A removal of the large fluctuations in the diameter o the amorphous column, preserving a narrow continuous column, is surprisingly discovered. Correlations with magnetization measurements demonstrate the greater efficiency of vortex pinning at 77K by the annealed defect structure.