Role of ZrO2/SnO2 Nano-Particles on Superconducting Properties and Microstructure of Melt-Processed Gd123 Superconductors

Bulk GdBa
₂
Cu
₃
O
_7–δ
(Gd123) superconductors were fabricated in air by adding ZrO
₂
/SnO
₂
nanoparticles with an average size of 50 nm. The effect of addition on microstructure and superconducting properties was investigated by scanning electron microscopy (SEM)/transmission electron microscopy (TEM) and SQUID. SEM results show that the distribution of Gd
₂
BaCuO
₅
(Gd211) particles is inhomogeneous around the seeding site of single domain, induced by the addition of nano-par-ticles. Particles with size less than 50 nm were observed by TEM inside Gd123 single domain, while the typical size of fined Gd211 particles is about 100 nm. Critical current density (
J_c
) was enhanced by the proper amount addition of ZrO
₂
/SnO
₂
additions. The highest
J_c
of 100,000 A/cm
²
was presently achieved in the bulk with 0.4 mol % ZrO
₂
, under self-field at 77 K. Excess amount addition rather suppresses superconducting properties. The optimum addition amount is 0.2-0.8 mol % for ZrO
₂
and 0.4-0.8 mol % for SnO
₂
, ratio to Gd123, respectively.