A modified multi-seeding approach for YBCO bulk superconductors using Y2BaCuO5 buffer process

• RE211 buffer was firstly applied to multi-seeded REBCO bulk superconductors.
• This approach is effective in reducing the impurity phases at the grain boundary.
• A single peak of trapped field can be observed in multi-seeded YBCO bulk.

We reported a modified multi-seeding approach to grow multi-seeded single grain Y–Ba–Cu–O (YBCO) bulk for overcoming the problem in conventional multi-seeding method, i.e. the existence of residual impurity phases (unreacted liquid phases and segregated RE2BaCuO5 phases) at the grain boundaries in the multi-seeded YBCO bulk. By inserting an Y2BaCuO5 (Y211) buffer between SmBa2Cu3O7−δ (Sm123) seeds and YBa2Cu3O7−δ (Y123)/Y211 compact, the multi-seeded YBCO bulk samples with Y211 buffer were grown successfully. A single peak of trapped field distribution with enhanced trapped field value can be observed in multi-seeded YBCO bulk sample with Y211 buffer. Microstructural studies show that the extent of residual impurity phases deposited at the grain boundary of the multi-seeded YBCO sample with Y211 buffer is significantly decreased compared with that of sample without Y211 buffer, which indicates that the buffer process is effective in decreasing the excluded phases formed at the grain boundaries in the multi-seeded bulk superconductor. The considerably suppression of the residual impurity phases can be qualitatively explained by the proximity effect of the seeds which is caused by the new buffer growth process similar to the seeded infiltration and growth (SIG) combined with the top seeded melt growth (TSMG).