Melt processing of bulk high Tc superconductors and their application

We report Melt-Powder-Melt-Growth(MPMG) process which results in high Jc for bulk Y-Ba-Cu-O superconductors. The Y-Ba-Cu-O pellets or powders are melt-quenched. The quenched plates are crushed into powder and mixed well. The powder is then compacted into desired shapes and remelted again and slowly cooled in thermal gradient. When the starting composition is changed from the 1:2:3 stoichiometry toward the Y2BaCuO5(211) rich region, the 211 inclusions can be dispersed in the YBa2Cu30x matrix, which contributes to the increase in both flux pinning force and fracture toughness. A Jc value exceeding 3xl08A/m2has been achieved at 77K and 1T. Another attractive feature of the MPMG process is that other component such as fine Ag powders can be added during solid-state mixing. Fine dispersion of Ag particles is effective to reduce the amount of cracking. MPMG processed Y-Ba-Cu-O with Ag doping can levitate a mass of 3kg at 1mm height using a repulsive force against a 0.4T magnet. Non-contacting rotation device such as magnetic bearing can be made utilizing bulk high Jc materials. Superconducting permanent magnet is also a promising candidate for future application. MPMG processed Y -Ba-Cu-O can generate 0.25T at 77K.