High transport critical current densities in textured Fe-sheathed Sr1−xKxFe2As2+Sn superconducting tapes

Abstract

Abstract:We report the realization of grain alignment in Sn-added Sr 1-x K x Fe 2 As 2 superconducting tapes with Fe sheath prepared by ex-situ powder-in-tube method. At 4.2 K, high transport critical current densities J c of 2.5×10 4 A/cm 2 (I c = 180 A) in self-field and 3.5×10 3 A/cm 2 (I c = 25.5 A) in 10 T have been measured. These values are the highest ever reported so far for Fe-based superconducting wires and tapes. We believe the superior J c in our tape samples are due to well textured grains and strengthened intergrain coupling achieved by Sn addition. Our results demonstrated an encouraging prospect for application of iron based superconductors.* Author to whom correspondence should be addressed; E-mail: ywma@mail.iee.ac.cn 2 The discovery of superconductivity in LaFeAsO 1-x F x and related compounds, with a higher transition temperature, T c of ~55 K, has triggered great research interests from both theoretical and applied aspects [1][2][3][4][5][6][7]. In addition to T c , these iron based superconductors were reported to have a very high upper critical field, B c2 , and low B c2 anisotropy, making them potential candidates for a wide array of future applications [8][9][10][11]. The early results indicate that the global critical current is limited by intergrain currents over the grain boundaries in polycrystalline bulk and wires [12][13][14][15][16][17][18]. Recent experiments revealed that high-angle grain boundary largely deteriorates critical current density J c in Ba(Fe 1-x Co x ) 2 As 2 bicrystals [19,20]. These results suggest that the discovered iron based superconductors are exhibiting weak link grain boundary behavior similar to high-T c cuprate superconductors. An effective method to overcome the weak link problem is to engineering textured grains in iron based superconductors to minimize deterioration of the critical current density across high-angle grain boundaries.Recently Co-doped Ba122 coated conductors have been grown by several groups utilizing the existing YBCO coated conductor technology and have reached a self-field J c over 1 MA/cm 2 [21][22][23]. However, the technology has the shortcoming of low production rate, complexity and high equipment cost. Furthermore, it is hard to be applied to the volatile elements in iron based superconductors such as alkali metals doped 122 phase and F doped 1111 phase. Cold deformation process is a well-developed technique used to enhance the degree of grain alignment and critical current density of Bi2223 superconductors [24,25]. It is unsurprising that this technique may also be suitable for iron based superconductors too. Besides grain alignment, adding metallic elements is another effective way to improve the grain connectivity of the iron based superconductors. For example, we have reported that the superconducting properties of the 122 phase iron based superconductor can be significantly increased by Ag or Pb addition [26,27]. Recently Togano et al [28] reported further improvement in transport critical current in the Ba122 wires with A...

Critical current density and magnetic phase diagrams of BaFe1.29Ru0.71As2single crystals

“…Successful synthesis of wires of substituted Ba122 superconductors [18,19] have recently been achieved and therefore optimisation of the current carrying capacity (J C ) will be useful.…”

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

“…The performance of IBS wires and tapes has been much improved by several methods, such as combination of several times of cold press and hot press [21] or only hot press [16,[22][23][24], only cold press [32,35], addition of metals like Ag, Pb, and Sn [25][26][27][28][29][30][31], or by texturing [27,30,31].…”

Role of heat and mechanical treatments in the fabrication of superconducting Ba0.6K0.4Fe2As2ex situpowder-in-tube tapes

“…Weiss et al [13] showed how high pressure applied on the wire during the heat treatment at relatively low temperature results in fine grains and enhancement of the superconducting core density and thus of Jc. The effectiveness of the texturing induced by rolling in Jc enhancement has been reported in ref.s [12,14]. More recently, many papers described how a combination of densification and texturing processes realised through uniaxial pressing [15,16] or hot pressing [17,18] allow to achieve Jc values of industrial interest.…”

“…The achievement of all these characteristics into a single wire represents a major technological breakthrough. Using the coated-conductor technology a Jc of 1MA/cm 2 has been measured in Co-doped BaFe2As2 grown on Fe/IBAD-MgO-buffered metal tape [9], however the most explored technique for wire manufacturing is the Powder In Tube (PIT) method [10,11,12]. Weiss et al [13] showed how high pressure applied on the wire during the heat treatment at relatively low temperature results in fine grains and enhancement of the superconducting core density and thus of Jc.…”