Recrystallization of YBazCu30x superconductors in vacuum

YBa2Cu30 x ceramics were recrystallized in vacuum at high temperatures. Recrystallized layers consisting of small grains were observed near the surfaces of the original large-grain 1 2 3 ceramics. The small grains consisted of transformation twins and were identified to ortho-rhombic 1 2 3 using X-ray diffraction. As vacuum annealing time increased, the thickness of the recrystallized layer increased. The relationship between the thickness and the annealing time showed a linear relationship and an effective diffusion coefficient of 6.25 x 10-1 ~ cm2s-1 The recrystallized layer showed a critical temperature of 90 K. 1. Introduct ion A high-T cceramic superconductor was discovered by Bednorz and Muller[l]. This discovery showed high-To superconductivity with the critical temper-ature of 35 K and opened a new field of oxide super-conductors. The discovery of Y-Ba-Cu-O supercon-ductor [2] with a To value of 93 K further stimulated the field, as liquid nitrogen could be used as a coolin