Enhanced high-field performance in Fe-sheathed MgB 2 tapes using inexpensive stearic acid additives
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Enhanced high-field performance in Fe-sheathed MgB2 tapes using inexpensive stearic acid additives Yanwei Ma,a) Zhaoshun Gao, Xianping Zhang, Dongliang Wang, and Zhengguang Yu Key Laboratory of Applied Superconductivity, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100080, China
K. Watanabe Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Haihu Wen Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
E. Mossang Grenoble High Magnetic Field Laboratory, C.N.R.S., 25, 38 042 Grenoble Cedex 9, France (Received 14 May 2007; accepted 26 July 2007)
High performance Fe-cladded MgB2 taps were prepared by the in situ powder-in-tube method utilizing very cheap stearic acid (C18H36O2) as dopants. The amount of stearic acid was varied from 0 to 30 wt%. We found that a significant enhancement of Jc, Hirr, and Hc2 in comparison with undoped samples was easily achieved. At 4.2 K, the transport Jc for the best doped tapes (10 wt%) reached 2 × 104 A/cm2 at 10 T and 3.7 × 103 A/cm2 at 14 T, respectively, an order of magnitude higher than for the pure tapes. In particular, at 20 K, the irreversibility field of the 10 wt% doped tape was around 10 T, which is comparable to the upper critical field of the commercial NbTi at 4.2 K. The results demonstrate great potential of MgB2 tapes for superconducting magnets.
The discovery of superconductivity at 39 K in the MgB2 compound has generated great interest in the field of applied superconductivity. Compared with conventional metallic superconductors (LTS), MgB2 has advantages of high-transition temperature (Tc) and low raw material costs of both B and Mg. MgB2 wires could become a credible competitor to LTS-based wires or to BiSrCaCuO (BSCCO)-based wires used in lowtemperature ( 50 T for C-doped MgB2 films.2 Such a value exceeds those of any Nb-based conductor at any temperature, suggesting that MgB2 could be a feasible replacement for Nb3Sn as a high-field magnet conductor. Indeed, superconducting MgB2 tape has been regarded as one of the most promising materials for the next generation of superconductor applications.3 Wires and tapes of MgB2 have been made
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0384 J. Mater. Res., Vol. 22, No. 11, Nov 2007
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using the so-called “powder-in-tube” (PIT) technique with encouraging results, e.g., we have recently shown that nanocarbon-doped MgB2 tapes have reached a critical current density Jc higher than 1000 A/cm2 at 4.2 K in a magnetic field of 14 T.4 However, the in-field Jc of MgB2 tapes and wires does not yet reach a practical level because of low upper critical field and poor flux pinning. To improve Jc–H properties of Fe-sheathed MgB2 tapes, a number of experimental techniques, including chemical doping, irradiation, and ball-milling methods, have been attempted.5–10 Among many methods, alloying with carbon seems to be the most effective to improve the propert
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