Fabrication of Gd-Ba-Cu-O bulk superconductors with a cold seeding method

The target of an unmanned space experiment is the fabrication of large grain Gd-Ba-Cu-O superconductors 12 cm in diameter in microgravity environment. The advantage of the space experiment is the support of a huge sample by a seed crystal alone. For this experiment, the cold seeding (CS) method must be employed to meet the requirements of the space program. Although the CS method is easy to apply, it has been difficult to grow large grain samples because of a small temperature window for a stable crystal growth. We thus studied the heat schedules for the space experiment using a prototype ground experiment furnace, which is similar to the furnaces launched into space. We could find the melt growth conditions that enabled us to successfully grow Gd-Ba-Cu-O bulk superconductors 10 cm in diameter even by the CS method.