HOMOGENEITY OF SUPERCONDUCTING PROPERTIES IN SMBA2CU3O7-DELTA SEEDED MELT-PROCESSED YBCO

The homogeneity of the superconducting properties of a large grain (2 cm diameter) YBa2Cu3O7-delta (YBCO) sample fabricated by SmBa2Cu3O7-de lta-seeded melt growth has been investigated in detail and correlated with variations in sample composition and microstructure. Magnetic cha racterisation of small (approximate to 8 mm(3)) individual specimens c ut from various positions in the bulk sample indicates a significant v ariation in the superconducting transition temperature, critical curre nt density and irreversibility field within the large YBCO grain. The transition temperature increases smoothly with sample radius to a dist ance of the order of several millimetres from the seed which correlate s well with an observed local Sm contamination of the YBCO matrix. The observed variation of the critical current density and irreversibilit y field with position is associated primarily with the reduced transit ion temperature in the vicinity of the seed, a degradation in the micr ostructure towards the sample edge and a variation in the Y2BaCuO5 inc lusion density with sample radius. (C) 1998 Elsevier Science S.A. All rights reserved.