  Material Science and Technology of Japan, 55㸦2018㸧77㹼81

Vol. 55 No. 235

Regular Paper
Superconducting Critical Current Densities for Sr2VFeAsO3-į Wires
Fabricated by ex-situ Powder-in-tube Process
Suguru IWASAKI1, Masanori MATOBA2 and Yoichi KAMIHARA2,*1

School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio
University, 3-14-1 Hiyoshi, Kohoku-Ku, Yokohama, Kanagawa 223-8522, Japan2

Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio
University, 3-14-1 Hiyoshi, Kohoku-Ku, Yokohama, Kanagawa 223-8522, JapanReceived Jan. 25, 2018; accepted for publication Mar. 20, 2018
Abstract
Superconducting wires were fabricated via an ex-situ powder-in-tube (PIT) process using a Fe/Ag bimetallic sheathas a sheath material and Sr2VFeAsO3-į as a core material. The superconducting wires were prepared by a solid-state
reaction in an evacuated quartz tube at 900°C for 1, 2, and 4 h after being rolled. The superconducting wires
exhibited zero resistivity at temperatures ≤ 8-12 K. Critical current densities (Jc) of the superconducting wires weredetermined from their V-I curves. The Jc was extrapolated up to 45.3 Acm-2 at 0 K for the 1 h-sintered wire.
Keywords: Iron-based superconductor, Perovskite-related structure, Superconducting wire, Sr2VFeAsO3-į.

1.

Introduction

complex superconducting materials. Indeed, a superconducting

Since the discovery of iron-based superconductor [1] in 2008,

thin film, which shows axially oriented crystallographic phaseseveral iron-based superconductors were discovered, such aswith a homogeneous chemical state, exhibits large Jc as well as

FeSe (11 phase) [2], Ae1-xKxFe2As2 (122 phases, Ae: Alkali earth

single crystalline superconducting samples. [26, 27]elements) [3], LiFeAs (111 phase) [4], ReFeAsO1-xFx (1111In order to enhance Jc, various approaches have beenphases, Re: rare earth elements) [1], and perovskite-related

reported to exclude the weak-link; e.g. additions of low melting

Sr2TMFePnO3-į (21113 phases, TM : transition metal elements, Pn

point metals such as Ag [11], Sn [17, 18], hot isostatic pressing= P, As) [5-7]. These iron-based superconductors exhibit(HIP) [12, 14], and an uniaxial pressing after flat rolling [13].

relatively high upper critical magnetic flux density at

The various approaches are tried to demonstrate both of axiallytemperatures (T) below superconducting transition temperatures

oriented crystallographic phase and homogeneous chemical state(Tc). Therefore, iron-based superconductors are promising forin a polycrystalline bulk samples for superconducting wires.
For the 1111 phases, a reactive solid state binder (RSB)

applications under high magnetic fields [8-10].
Several researchers have reported superconducting wiresmethod was employed to compensate the loss of F during heatusing 122 [11-16], 1111 [17-21] and 11 [22, 23] phases as coretreatments in 2011. The superconducting wires fabricated bymaterials via powder-in-tube (PIT) process [10], although

RSB method reached 4000 Acm-2 at 4.2 K under a magnetic flux

superconducting

thedensity (μ0H) = 0.03 T [19, 20]. In recent, Jc of superconducting

superconducting wires have been lower than those oftapes increased to 3.95 × 104 Acm-2 at 4.2 K under self-field [17],superconducting single crystalline samples. Such a lowering of Jc

to 1.8 × 104 Acm-2 at 4.2 K under μ0H = 0.6 T, and to 2.9 × 102

is called as a weak-link. The weak-link is mainly due to twoAcm-2 at 4.2 K under μ0H = 10 T [18] by low-temperaturefactors. A factor is a decreasing of Jc due to grain boundaries’

synthesis with Sn adding. For the 122 phase, various chemicalgeometry. [24, 25] The other factor is an inhomogeneous and acompositions such as Ba1-xKxFe2As2 [14], Sr1-xKxFe2As2 [15], andphase segregated chemical states that are often observed forSr 1-x Na x Fe 2 As 2 [16] were employed for the fabrication ofcriticalcurrent

densities

(Jc)

of

*Corresponding author: kamihara_yoichi@keio.jp(77)