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 (<formula><tex>$J_{c}$</tex></formula>) and high trapped magnetic fields, which is attributed to the presence of pinning centers such as micro-sized <formula><tex>${\rm Y_{2}BaCuO_{5}}$</tex></formula> (Y211) inclusions. The introduction of nano-sized particles is known to function as more effective pinning centers than micro-sized ones. It has been reported that <formula><tex>$J_{c}$</tex></formula> values were enhanced with the addition of nano-sized particles such as <formula><tex>${\rm ZrO_{2}}</tex></formula> and <formula><tex>${\rm Y_{2}Ba_{4}CuMO_{y}}$</tex></formula> (M = Nb, Zr, etc.) in the <formula><tex>${\rm YBa_{2}Cu_{3}O_{x}}$</tex></formula> (Y123) matrix. We have focused on nanocarbon as another candidate of the pinning center and reported that the addition of carbon nanotube (CNT) and nanodiamond led to the enhancement of <formula><tex>$J_{c}$</tex></formula> in Y-Ba-Cu-O superconductors. Fullerene (<formula><tex>${\rm C_{60}}$</tex></formula>) is also expected to improve the flux pinning performance. We then fabricated melt-processed Y-Ba-Cu-O bulk samples with the addition of fullerene and investigated the pinning properties and microstructures. SEM observation showed that nano-sized particles were distributed in the Y123 matrix. <formula><tex>$J_{c}$</tex></formula> exhibited the highest values for the sample with 1.0 wt% fullerene addition. These results suggest that fullerenes act as effective pinning centers.