Y2BaCuO5 buffer block as a diffusion barrier for samarium in top seeded melt growth processedYBa2Cu3O7 − y superconductorsusing a SmBa2Cu3O7 − d seed

Abstract

A Y2BaCuO5 buffer(Y211) block, as a diffusion barrier for samarium atoms of a top seeded melt growth (TSMG) processedYBa2Cu3O7 − y (Y123) superconductorusing a SmBa2Cu3O7 − d (Sm123) seed, was examined in terms of the buffer thickness (t). Disc-type Y211blocks with various t were inserted at the seed/compact interface and subjected to meltgrowth heating cycles. The superconducting transition temperature (Tc) and criticalcurrent density (Jc) were measured for the three different top surface regions: (1) the region justbelow the seeded Y211 buffer block, (2) the intermediate region betweenthe buffer block and the sample edge, and (3) the sample edge. TheTc values of regions 1 and 2 of the samples without the buffer and with thin buffers were lowerthan that of region 3, and the superconducting transition widths were larger. Ast was increased to 3 mm, the susceptibility curves of the three regions showed the sameTc of 90 K and sharptransitions. The Jc–B curves of regions 1 and 2 without a buffer and with thin buffers showed the peak effect due to the formation ofY1 − xSmxBa2Cu3Oz. The peak effect almostdisappeared when t was increased to 3 mm. Y211 particles and the Y123 matrix in the buffer block acted asan effective samarium absorber by forming mixed rare-earth 211 particles andY1 − xSmxBa2Cu3Oy. These results suggest that the Y211 buffer block technique can be applied tothe fabrication of large single grain Y123 superconductors with a uniformTc andJc distribution on the top surfaces.