Fabrications and evaluations of critical current density of (Ba,Na)Fe2As2 HIP round wires

Enhancement of critical current density in (Ba,Na)Fe2As2 round wires using high-pressure sintering

“…It should be noted that the HIP wire using the powder mixed by ball milling method and sintered at 800 • C also shows large transport J c ∼ 38 kA cm −2 under 100 kOe at 4.2 K (data not shown). These values are larger than the value of previous studies on (Ba,Na)Fe 2 As 2 wires [ [46][47][48]. Furthermore, the transport J c of the #1 wire under 100 kOe slightly exceeds the previous largest value of transport J c (∼38 kA cm −2 ) among all round wires achieved in (Ba,K)Fe 2 As 2 [32].…”

“…Compared with former studies on (Ba,Na)Fe 2 As 2 wires [46][47][48], the quality of prepared polycrystalline powders for raw materials of wires and superconducting properties of HIP wires are significantly improved in the present study. There are several differences of powder synthesis process of the #2 powder compared with of powder in the previous study [46,48], such as the increase in sintering temperature from 770 o C to 820 o C, the increase in the additional NaAs content α from 0.05 to 0.1, the reduction of a number of sintering from twice to once.…”

“…Compared with former studies on (Ba,Na)Fe 2 As 2 wires [46][47][48], the quality of prepared polycrystalline powders for raw materials of wires and superconducting properties of HIP wires are significantly improved in the present study. There are several differences of powder synthesis process of the #2 powder compared with of powder in the previous study [46,48], such as the increase in sintering temperature from 770 o C to 820 o C, the increase in the additional NaAs content α from 0.05 to 0.1, the reduction of a number of sintering from twice to once. The #1 powder and related powders, in which raw elements had been mixed by ball milling method, were also fired only once at a higher temperature of 800 ∼ 900 o C. Considering these differences of synthesis conditions and the fact that the analyzed Na content is less than the nominal content of x, sintering at above 800 o C for a long enough time and the compensation of the loss of Na during the synthesis have played key roles for preparing (Ba,Na)Fe 2 As 2 powders with negligible impurities.…”

“…Onsets of diamagnetization of both the #1 and #2 powders were detected at approximately 34.5 K as shown in figure 1(a). Although the drop of the magnetization of the #1 powder is slightly sharper than that of the #2 powder, reasonably sharp transition indicates that the quality of both powders are higher than the previous study [46][47][48]. XRD patterns of the #1 and #2 powders shown in figure 1(b) have strong peaks of (Ba,Na)Fe 2 As 2 phase and do not show peaks of impurities such as FeAs or Fe 2 As.…”

“…The transport J c for (Sr,Na)Fe 2 As 2 tapes of 26 kA cm −2 at 4.2 K under 100 kOe, and that for (Ba,Na)Fe 2 As 2 tapes of 40 kA cm −2 at 4.2 K under 40 kOe, were also reported [42,45]. Very recently, J c in (Ba,Na)Fe 2 As 2 HIP round wire reached 150 and 20 kA cm −2 at self-field and 100 kOe, respectively [46][47][48]. These values are more than fifty percent of the largest J c in (Ba,K)Fe 2 As 2 round wires, demonstrating the excellent performance of (Ba,Na)Fe 2 As 2 wires.…”