Effects of drawing and high-pressure sintering on the superconducting properties of (Ba,K)Fe₂As₂powder-in-tube wires

Abstract

The evolution of the superconducting properties of round wires of (Ba,K)Fe 2 As 2 fabricated by the powder-in-tube (PIT) method is systematically studied. After establishing the method to obtain the largest transport critical current density (J c ) in round wires using the hot isostatic press technique, we investigated how the transition temperature (T c ), J c , and microstructures change at each step of the wire fabrication. Unexpectedly, we find that superconducting properties of the wire core are significantly damaged by the drawing process. Systematic measurements of J c and T c of the core superconductor after each drawing and sintering process clarified the evolution of degradation by the drawing process and recovery by heat treatment. Keywords: superconducting wires, hot isostatic pressing (HIP), (Ba,K)Fe 2 As 2 , powder-in-tube (PIT), critical current density, effects of drawing and sintering

Enhancement of critical current densities in (Ba,K)Fe2As2wires and tapes using HIP technique

“…T c in both the HIP wire and tape is approximately 36 K. The small reduction of T c after the wire fabrication is almost the same compared with the previous reports on the HIP wires with the highest J c [21,39]. This T c reduction is caused by the degradation in the drawing process and incomplete recovery by the successive sintering, as discussed in ref [39]. Shielding volume fractions of the HIP wire and tape are roughly 100% and 1300%, respectively, at 10 K. The overestimated volume fraction of the HIP tape over 100% is caused by the demagnetization effect of the tape shape.…”

“…Figure 1 shows the temperature dependence of magnetization for both the HIP wire and tape. T c in both the HIP wire and tape is approximately 36 K. The small reduction of T c after the wire fabrication is almost the same compared with the previous reports on the HIP wires with the highest J c [21,39]. This T c reduction is caused by the degradation in the drawing process and incomplete recovery by the successive sintering, as discussed in ref [39].…”

“…Although the HIP method has been applied for the fabrication of 122-type superconducting round wires, the reported values of J c is not high enough. At present, J c in both (Ba,K)Fe 2 As 2 and (Sr,K)Fe 2 As 2 HIP wires achieved approximately 100 kA/cm 2 at 4.2 K under self-field [21,23,39,40]. However, their J c at high magnetic fields is reduced to below 20 kA /cm 2 .…”

“…Mainly, two pressing methods for the fabrication of IBS wires and tapes have been proven to be effective in enhancing J c , namely, uniaxial pressing for the tape [32][33][34][35][36] and hot isostatic pressing (HIP) for round wires [21,23,39,40]. Although uniaxial-press method has realized the highest J c value, it cannot be used for the fabrication of round wires.…”

Highly c-axis orientated superconducting core and large critical current density in Ba0.6Na0.4Fe2As2 powder-in-tube tape

“…The degradation in T c after wire/tape fabrication process has been also reported in previous works 23 . An explanation for the reduction in T c is the loss of Na during the fabrication process, although the Na concentration is seemingly unchanged within the resolution of the XRD and the EDX measurements.…”