Abstract
Buffer-aided top seeded infiltration and growth (TSIG) with a suitable liquid phase reservoir has been compared with the top seeded melt growth (TSMG) process and applied successfully to fabricate single grain YBa2Cu3O7-δ(YBCO) bulk superconductors. A Yb-based liquid phase has been observed to yield the homogeneous, high density YBCO single grains by the TSIG technique. Sintering the Y2BaCuO5(Y-211) preform prior to TSIG has been found to be critical in retaining the shape of the sample during the infiltration and growth process. A number of advantages of the TSIG process have been demonstrated, including a dramatic reduction in sample shrinkage and a general improvement in bulk microstructure. TSIG processed samples also exhibit a fine and even distribution of unreacted, embedded Y-211 inclusions that play a key role in flux pinning in the fully processed bulk material. A YBCO sample of diameter 25mm fabricated by the optimised buffer-aided TSIG process was able to trap a field of 0.63T at 77K, which is the highest value of trapped field ever reported for a YBCO sample fabricated by the TSIG process. The technique reported here has the potential to improve further the microstructural and superconducting properties of single grain bulk YBCO, which enhances further the applications potential of these materials.
Highlights
Bulk (RE)Ba2Cu3O7-␦(RE)BCO superconductors processed in the form of large, single grains can carry large critical currents and are potentially useful for application as trapped field magnets and in motors and generators etc. [1,2,3]
We propose an approach to top seeded infiltration and growth (TSIG) process that emerged after a detailed investigation carried out on each of the components for TSIG
We report an adaptation of the buffer technique [7] to improve the reliability of the single grain growth process
Summary
Bulk (RE)Ba2Cu3O7-␦(RE)BCO superconductors processed in the form of large, single grains can carry large critical currents and are potentially useful for application as trapped field magnets and in motors and generators etc. [1,2,3]. There are significant challenges associated with these techniques [10,11,12] such as sample shrinkage, porosity, the presence of voids, the formation of large cracks, the generation of large-sized (RE)2BaCuO5 (RE-211) with an acicular morphology and inhomogeneity in the distribution of RE-211 inclusions within the (RE)Ba2Cu3O7-␦ (RE-123) superconducting matrix Most of these defects occur as a result of outflow of liquid phase from the bulk sample during the melt process [11]. Li and Yang et al [24,25,26] reported that a liquid phase comprising of Y2O3, CuO and BaCuO2 (mixed 1:6:10 by molar ratio) enables the effective growth of RE-123 single grain, bulk superconductors These authors proposed that a new, solid phase comprising of RE2O3 and BaCuO2 can be used instead of the conventional RE-211 for the preform composition in the TSIG process. Buffer-aided TSIG avoids shrinkage and aids the homogeneity of Y211 inclusions in the superconducting matrix when compared to the conventional TSMG process
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