Superconducting critical current density enhanced to 285 A cm^-2 for Sr₂VFeAsO_3-δ tapes fabricated by ex situ powder-in-tube process

Superconducting critical current density (J _c) at 4.2 K for superconducting Sr₂VFeAsO_3-δ tape fabricated by powder-in-tube process was enhanced up to 285 A cm^-2. Cross-sectional SEM images for superconducting Sr₂VFeAsO_3-δ wire/tapes indicated that void fraction f _void was reduced from 12.8% for the round wire to ∼2.5% for the tapes. The decrease in f _void suppresses the so-called "weak-links" and therefore enhances the J _c. In order to enhance J _c, the annealing condition should be optimized. The optimal annealing condition enforces the link between grains and avoids the loss of oxygen atoms in the superconducting core.