Bi:2212 Multifilamentary Round Wires -- Intrinsic and Extrinsic J_c Limitations, Comparison to Monocrystal Properties

Abstract

Bi:2212 round multifilamentary wires with 259 filaments and filament diameters (d_f) of 30 and 11 μm have been fabricated and evaluated. Transport J_c values as high as 1.68 × 10⁵ A/cm² (normalized to superconductor area) have been obtained at 4.2 K and self field for wires with a d_f of 11 μm. Transition temperatures (T_c), reversibility fields (H_r), pinning well depths (U₀), magnetic- (J_cm), and transport critical current densities (J_ct) were measured and compared to values measured for single crystals and 3-D textured melt grown samples. H_r and U₀ values were quite similar for all wires, as well as in comparison to the 3-D textured crystalline values, although T_c was somewhat lower in the wires. J_cm was similar for the wires and the 3-D textured samples, both of which had somewhat higher J_cms than that of the single crystal. Additionally, transport J_c (which was not measured for the crystalline samples) varied considerably in the wires. Intrinsic and extrinsic variations were considered for this discrepancy. A possible source of the J_c variation with d_f is a variation of the fraction of well aligned material with filament size. Additionally, some degradation of filament quality is observed with decreasing d_f, increasing the variability of measured J_ct.