Effects of Fullerene Addition on Pinning Properties and Microstructures in Melt-Textured Y-Ba-Cu-O Superconductors

Bulk Y-Ba-Cu-O superconductors have significant potential for engineering applications due to high critical current density (J_c) and high trapped magnetic fields, which is attributed to the presence of pinning centers such as micro-sized Y₂BaCuO₅ (Y211) inclusions. The introduction of nanosized particles is known to function as more effective pinning centers than micro-sized ones. It has been reported that J_c values were enhanced with the addition of nanosized particles such as ZrO₂ and Y₂Ba₄CuMO_y (M = Nb, Zr, etc.) in the YBa₂Cu₃O_x (Y123) matrix. We have focused on nanocarbon as another candidate of the pinning center and reported that the addition of carbon nanotube (CNT) and nanodiamond led to the enhancement of J_c in Y-Ba-Cu-O superconductors. Fullerene (C₆₀) is also expected to improve the flux pinning performance. We then fabricated melt-processed Y-Ba-Cu-O bulk samples with the addition of fullerene and investigated the pinning properties and microstructures. SEM observation showed that nanosized particles were distributed in the Y123 matrix. J_c exhibited the highest values for the sample with 1.0 wt% fullerene addition. These results suggest that fullerenes act as effective pinning centers.