Chemical stability and superconductivity in Ag-sheathed CaKFe₄As₄ superconducting tapes

Abstract

Ag-sheathed CaKFe4As4 superconducting tapes have been fabricated via the ex-situ powder-in-tube method. Thermal and X-ray diffraction analyses suggest that the CaKFe4As4 phase is unstable at high temperatures. It decomposes into the CaAgAs phase which reacts strongly with the silver sheath. We therefore sintered the tape at 500 °C and obtain a transport critical current density Jc(4.2 K, 0 T)~ 2.7 × 10 4 A/cm 2 . The pinning potential derived from magnetoresistance measurements is one order of magnitude lower than that of the (Ba/Sr)1-xKxFe2As2 tapes. Combining with the scanning electron microscopy and magneto-optical imaging results, we suggest that bad connectivity between superconducting grains caused by the low sintering temperature is the main factor responsible for the low Jc. However, this system is still a promising candidate for superconducting wires and tapes if we further optimize the post-annealing process to achieve better grain connectivity.

Optimization of superconducting properties of the stoichiometric CaKFe4As4

“…The calculated J c for and the field dependence of J c for samples prepared at different synthesis temperature are shown in Figure 7(b). We find higher J c values for the optimum sample compared to the values for the other samples being also similar to that reported value for 1144 wires and tapes 14,15 . The field dependence of J c behaviour for all samples is similar, decreasing rapidly at low fields but becoming weakly field dependent at high fields.…”

Tuning the Intrinsic Anisotropy with Disorder in the CaKFe4As4 Superconductor

“…In addition, it has been pointed out that keeping the stoichiometric composition of CaK1144 is by itself a strong advantage in the production process of wires and tapes [11] and ion irradiation allows us to tune several properties while keeping the stoichiometry fixed.…”

“…Specifically, the anisotropy parameter that enters the anisotropic Ginzburg-Landau (AGL) scaling relation for the angle-dependent critical current has been shown to behave just as γ λ for MgB 2 [9] and Fe(Se,Te) [8] and as γ H for Ba(Fe, Co) 2 As 2 [10]. In addition, vortex pinning and anisotropy place fundamental restrictions on the current-carrying capability of materials [11] and therefore a way to engineer them is required.…”

Superconducting critical current density enhanced to 285 A cm−2 for Sr2VFeAsO3−δ tapes fabricated by ex situ powder-in-tube process

“…ron−based superconducting wires/tapes with superconducting critical temperature (T c ) > 20 K fabricated via the powder−in−tube (PIT) process, 1) were reported for ReFeAsO 1−x F x 2-4) (Re: Rare earth elements), Ae 1−x A x Fe 2 As 2 [5][6][7][8] (Ae: Alkali earth elements, A: Alkali elements), AeAFe 4 As 4 [9][10][11] and Sr 2 VFeAsO 3−δ . 12) In addition, superconducting tapes using FeSe 1−x Te x were reported 13,14) as well, though their T c s were lower than 20 K. Although the T c s of these iron−based superconductors are lower than those of cuprate superconductors, their upper critical magnetic fields (μ 0 H c2 ) are comparable.…”

“…In order to deny the effect of the polissing to f void , a Vickers hardness of the wire/tape should be evaluated. 10,11) Here, we discuss the cause of enhancement of J c from 45 A cm −2 for the round wire 12) to 285 A cm −2 for the tape. The experimental differences between the round wire 12) and the tape both sintered at 900 °C for 60 min were (i) rolling process for the composite (round wire or tape) and (ii) polycrystalline Sr 2 VFeAsO 3−δ powder.…”