Seed-Size Effect on the Growth and Superconducting Performance of YBCO Single-Grain Bulks

Abstract

Exploiting their distinguished merits of commercial availability, large size, and extremely high thermal stability, a series of NdBCO film-seeds were employed to study their size effects on the YBCO bulks by melt-growth. First, our findings show that the nucleation range is almost the same with the variation of the seed size and that the effective contact area of the seed with the molten pellet is smaller than the seed area, which can be explained by the liquid’s wettability and its surface energy. Moreover, induced by the large-sized seed, the YBCO grain has the highest a-axis growth rate, Ra, because of a double mode of thermally driven plus seed-induced growth, leading to a larger c-GS (c-growth sector). Finally, the levitation force of bulks were proven to possess an ascending and subsequently descending tendency with increasing the seed size, which is clarified by the enlargement of c-GS in competition with enhancement of pore density of bulks. In short, the results from this work are helpful to understand the crystallization mechanism and to gain the optimal superconductivity property with a reasonable seed size.