Abstract
The “peak effect” was observed in the J c -vs-H characteristics of an YBCO superconducting bulk melt-grown under varying oxygen partial pressure. “Large-area TEM” observations were performed for TEM specimens with an observable area as wide as 20μm x 20μm (and ∼ l00nm thickness) which were prepared using a focused ion beam (FIB) mill. More than 200 Y-211 particles were measured and the distributions of the Y-211 particles in two bulk samples which were post-annealed with different programs were nearly identical, though their J c characteristics were different. Therefore, very fine Y-211 particles are likely not to affect the J c value of the melt-processed YBCO bulks at high magnetic fields. On the other hand, a significant microstructural difference was recognized in the spacing between twin boundaries. The twin boundaries might have played a role of effective pinning centers under high magnetic fields (between 1 and 4 T) in the melt-grown YBCO superconducting bulks.
Published Version
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