Superconducting Properties of Welded Three Top‐Seeded YBa₂Cu₃O_7−<i>x</i> Produced with NdBCO/YBCO/MgO Thin‐Film Seed

This study investigates hollow single‐crystal top‐seeded melt growth (TSMG) YBa 2 Cu 3 O 7− x (YBCO or Y123) samples welded with Ag‐added TSMG YBCO solder materials produced using NdBCO/YBCO/MgO thin‐film seeds. Three main samples and one solder material are produced by the TSMG method. In order to increase the dimensions of the bulk YBCO superconductor, two slices of the solder material and the main samples are stacked on top of each other with the c ‐axis parallel and welded at 1030 °C. X‐ray diffraction patterns, polarized optical photographs, and SEM micrographs are taken to determine the structural properties of the samples. A preferential orientation in the c ‐axis is observed with a good connection. Low‐temperature resistance and magnetization measurements are made for the specimens taken from the welding region. A sharp superconducting transition occurs at 0 T around 93 K for welding regions of W‐ab and W‐bc specimens. The critical current densities ( J c ) are high as in the main samples. At the same time, the J c values at 77 K and 0 T are found as 1.54 × 10 4 , 1.98 × 10 4 , 2.21 × 10 4 , 2.31 × 10 4 , and 2.36 × 10 4 A cm −2 for the W‐a, W‐ab, W‐b, W‐bc, and W‐c specimens, respectively. The single‐grain feature is not impaired; thus, the absence of additional grain boundaries facilitates the current passage.