Study of the trapped field distributions and the microstructure for YBCO disks

The trapped field distributions on the surface of MTG YBCO disks were measu red by a Hall probe automated scanning system, and exhibit a cone profile f or sample A with levitation force up to 12.6 N/cm(2), whereas four peaks fo r sample B with 4.4 N/cm(2). However, c-axis orientations of two samples ar e all perpendicular to the sample surfaces according to the pole figure. Fo r sample B, the boundaries between the sectors seem to be weak links, and t he T-c in the sector, which is very low, is higher than that in the boundar y. The microstructure reveals that the agglomerates of non-superconductive phases occur in the boundary and the center for sample B, but do not occur in the sectors of sample B and nor in any part of sample A. So, it can be a ssumed that the agglomerates of non-superconductive phases in the boundary are mainly responsible for the low levitation force and trapped field with four peaks in distribution of sample B. (C) 2000 Published by Elsevier Scie nce B.V.