L. H. Jin

37-filamentary Bi₂Sr₂Ca₂Cu₃O_10+δ (Bi-2223) superconducting tapes were prepared by the powder-in-tube (PIT) technique. Leakage occurring during high-temperature processing is a major issue that degrades both the engineering critical current density (Jₑ) and mechanical properties of Bi-2223 conductors. In this work, the critical silver sheath thickness required to eliminate leakage was systematically investigated by correlating leakage behavior with local sheath thickness in different tapes. The results demonstrate that the leakage can be effectively eliminated when the silver sheath thickness exceeds 38 μm, which is identified as the critical threshold. Furthermore, increasing the wall thickness of the outer Ag alloy tube is shown to be an efficient approach for producing optimized Bi-2223 superconducting tapes. When the wall thickness of the outer Ag-alloy tube is increased from 0.6 mm to 0.8 mm or greater, the silver sheath thickness in the tapes exceeds 42 μm, which was above the critical value required for leakage suppression. These findings provide a practical guideline for reducing leakage in Bi-2223 tapes and offered a viable strategy applicable to other multifilamentary superconducting tapes and wires.

The mechanical response of Bi-2223 multi filamentary superconducting wires during cold drawing directly affects filament integrity and overall performance. A homogenized finite element model based on the mixture theory was established to describe the elastic–plastic behavior of Bi 2223/Ag composite wires. Drawing processes for 37, 55, and 121 filament architectures were analyzed under realistic die–wire contact conditions. The simulations show a pronounced radial stress gradient, with outer filaments carrying higher loads. As the filament number increases, load sharing becomes more uniform and the overall stress concentration decreases. Quantitative analysis of filament distortion indicates that increasing the filament count improves structural uniformity but also enhances the sensitivity to local imperfections. The proposed modeling framework provides a reliable basis for optimizing wire architecture and drawing parameters to improve the mechanical stability and superconducting performance of Bi-2223 wires.

Bi₂Sr₂CaCu₂O _x (Bi-2212)/Ag round wires prepared by the powder-in-tube method is a promising high-temperature superconductor for ultra-high field applications. The current capacity of Bi-2212/Ag wires is negatively affected by the impurity phase of Bi₂Sr₂CuO _x (Bi-2201). In this work, a novel precursor powder fabrication technique was developed to eliminate the presence of large residual Bi-2201 grains and to enhance the critical current density (J _c) of Bi-2212/Ag wires. Bi-2212 incorporating (Sr, Ca)₁₄Cu₂₄O _y (14:24AEC) precursor powders was prepared using a combination of ultrasonic spray pyrolysis and calcination processes. The influence of the 14:24AEC phase on the phase, microstructure, melting behavior and superconducting properties of Bi-2212/Ag wires was systematically investigated. During the overpressure heat treatment, the addition of 14:24AEC into the wire promoted melting, effectively reducing the formation of large Bi-2201 grains. Moreover, the formation of narrow Bi-2201/Bi-2212 intergrowth and stacking faults were introduced into the Bi-2212 matrix. The Bi-2212/Ag wire with added 2 wt% 14:24AEC exhibited a maximum J _c of 4670 A mm⁻² at 4.2 K and 12 T. Therefore, precise tuning of the alkaline earth cuprate composition in precursor powders could be a valid approach for improving the current capacity of Bi-2212/Ag multi-filamentary wires.

High-performance precursor powders are crucial for the transport current of Bi ₂ Sr ₂ CaCu ₂ O _x (Bi-2212) round wires. However, the impact of the powder calcination process on the wire performance is not fully understood. Here, Bi-2212 precursor powders were prepared using ultrasonic spray pyrolysis technique and then calcined under different atmospheres. The influences of calcination atmosphere on the microstructures, melting behavior and critical current density ( J _c ) of Bi-2212 multi-filamentary wires were systematically discussed by tuning the oxygen partial pressure from 0.001 bar to 1.0 bar. As the oxygen partial pressure was increased, a more uniform melting behavior was observed in the Bi-2212 wires, and the large merging bridges was reduced in the filaments. High J _c of 2715 A/mm ² at 4.2 K, 12 T were achieved in the sample with 1.0 bar O ₂ . Therefore, controlling calcination atmosphere of precursor powder was significant for achieving superior transport current of Bi-2212 wires.