Y2BaCuO5 buffer block as a diffusion barrier for samarium in top seeded melt growth processed YBa2Cu3O7-y superconductors using a SmBa2Cu3O7-d seed

A Y2BaCuO5 buffer (Y211) block, as a diffusion barrier for samarium atoms of a top seeded melt growth (TSMG) processed YBa2Cu3O7-y (Y123) superconductor using a SmBa2Cu3O7-d (Sm123) seed, was examined in terms of the buffer thickness (t). Disc-type Y211 blocks with various t were inserted at the seed/compact interface and subjected to melt growth heating cycles. The superconducting transition temperature (T-c) and critical current density (J(c)) were measured for the three different top surface regions: (1) the region just below the seeded Y211 buffer block, (2) the intermediate region between the buffer block and the sample edge, and (3) the sample edge. The T-c values of regions 1 and 2 of the samples without the buffer and with thin buffers were lower than that of region 3, and the superconducting transition widths were larger. As t was increased to 3 mm, the susceptibility curves of the three regions showed the same T-c of 90 K and sharp transitions. The J(c)-B curves of regions 1 and 2 without a buffer and with thin buffers showed the peak effect due to the formation of Y1-xSmxBa2Cu3Oz. The peak effect almost disappeared when t was increased to 3 mm. Y211 particles and the Y123 matrix in the buffer block acted as an effective samarium absorber by forming mixed rare-earth 211 particles and Y1-xSmxBa2Cu3Oy. These results suggest that the Y211 buffer block technique can be applied to the fabrication of large single grain Y123 superconductors with a uniform T-c and J(c) distribution on the top surfaces.