Masato Murakami

Progress in melt processing of Nd-Ba-Cu-O superconductors

Light rare earth (LRE)-Ba-Cu-O (LREBCO) bulk superconductors melt-processed in a reduced oxygen atmosphere considered to be very promising materials a high field operative with the liquid nitrogen because of their large critical current density (J/sub c/) in high magnetic fields at 77 K, surpassing the limitation of an optimized Y-Ba-Cu-O (YBCO) bulk superconductor. For obtaining further improved J/sub c/ and a large textured domain in the Nd-Ba-Cu-O system (Nd-system), we have applied the oxygen-controlled-melt-growth (OCMG) process to both directional and non-directional solidification techniques. At 77 K and for the field parallel to the (H//c), while J/sub c/ in low field region was apparently enhanced by refining the Nd/sub 4/Ba/sub 2/Cu/sub 2/O/sub 10/(ND422) second phase particles trapped in the NdBa/sub 2/Cu/sub 3/O/sub 7/ (Nd123) matrix, J/sub c/ in high field region principally depended on the location of the fishtail peak (H/sub pk/) which was sensitive to the PO/sub 2/ and thermal processing conditions during the melt growth. Problems related to the NdBCO domain enlargement are also discussed.

Seeded Melt Growth of Large LRE-Ba-Cu-O Bulk Superconductors

Grain enlargement of light rare earth (LRE)-Ba-Cu-O (LREBCO) bulk superconductors has been systematically investigated with the top-seeded melt growth (TSMG) method. The (001) cleavage surfaces of melt-processed NdBCO seed crystals were used for achieving c-axis oriented LREBCO single grains. For the Nd-Ba-Cu-O system, Ag addition was necessary to ensure a temperature margin for seeding since the peritectic decomposition temperature of NdBa2Cu3Oy (Ndl23) decreases with Ag addition, while the NdBCO seeds were effective for other LRE-Ba-Cu-O systems. Careful study on the seeded melt growth at various undercoolings (ΔT) enabled us to successfully fabricate large c-axis oriented NdBCO-Ag or SmBCO single grains in air. The growth rates R of SmBCO are faster than that of YBCO at the same ΔT.