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Epitaxial thin film seeds, exhibit a higher peritectic temperature than the bulk, have been recognized as a possible way to obtain large-sized single-grain REBCO bulks. Recently, use of a pellet as a buffer layer inserted between the film-seed and the main pellet has been reported. This approach can prevent Mg diffusion from the MgO substrate to the film seed, and enable the thin film to tolerate a higher maximum temperature in the TSMG (Top Seed Melt Growth) method. However, we found that the liquid phase decomposed from YBa2Cu3O7− x( YBCO) contacted the MgO substrate, due to surface tension, and caused undesirable grain nucleation. To resolve this problem, this study used a mini-pellet, smaller than the seed, as a buffer layer. This new technique can avoid the liquid phase contacting the MgO substrate, thereby allowing the YBCO single-grain bulk to be grown more easily. Moreover, the thin film seed can be re-used by removing the buffer layer after the crystal growing process. [ABSTRACT FROM AUTHOR]