Homogeneity of superconducting properties in SmBa2Cu3O7 − δ-seeded melt processed YBCO

The homogeneity of the superconducting properties of a large grain (2 cm diameter) YBa2Cu3O7-δ (YBCO) sample fabricated by SmBa2Cu3,O7-δ-seeded melt growth has been investigated in detail and correlated with variations in sample composition and microstructure. Magnetic characterisation of small (≈ 8 mm3) individual specimens cut from various positions in the bulk sample indicates a significant variation in the superconducting transition temperature, critical current density and irreversibility field within the large YBCO grain. The transition temperature increases smoothly with sample radius to a distance of the order of several millimetres from the seed which correlates well with an observed local Sm contamination of the YBCO matrix. The observed variation of the critical current density and irreversibility field with position is associated primarily with the reduced transition temperature in the vicinity of the seed, a degradation in the microstructure towards the sample edge and a variation in the Y2BaCuO5 inclusion density with sample radius.