189 research outputs found
Enhanced critical current density of MgB2 superconductor synthesized in high magnetic fields
The effect of high magnetic fields on the current carrying properties of both
MgB2 bulks and Fe-sheathed tapes was investigated following different thermal
sequences. It is found that application of a large magnetic field during
processing results in the quite uniform microstructure and the better
connectivity between the MgB2 grains. As a result, the Jc of these samples has
shown much higher value than that of the MgB2 samples in the absence of
magnetic field. The possible mechanism of the Jc enhancement under an external
magnetic field is also discussed.Comment: Presented at ISS2005, Tsukuba, 24-26 Oct., 2005; Revised versio
Significantly enhanced critical current densities in MgB2 tapes made by a scaleable, nano-carbon addition route
Nanocarbon-doped Fe-sheathed MgB2 tapes with different doping levels were
prepared by the in situ powder-in-tube method. Compared to the undoped tapes,
Jc for all the C-doped samples was enhanced by more than an order of magnitude
in magnetic fields above 9 T. At 4.2 K, the transport Jc for the 5 at% doped
tapes reached 1.85x104 A/cm2 at 10 T and 2.8x103 A/cm2 at 14 T, respectively.
Moreover, the critical temperature for the doped tapes decreased slightly.
Transmission electron microscopy showed a number of intra-granular dislocations
and the dispersed nanoparticles embedded within MgB2 grains induced by the C
doping. The mechanism for the enhancement of flux pinning is also discussed.
These results indicate that powder-in-tube-processed MgB2 tape is very
promising for high-field applications.Comment: 13 pages, 5 figures. to be published soo
Development of Powder-in-Tube Processed Iron Pnictide Wires and Tapes
The development of the PIT fabrication process of iron pnictide
superconducting wires and tapes has been carried out in order to enhance their
transport properties. Silver was found to be the best sheath material, since no
reaction layer was observed between the silver sheath and the superconducting
core. The grain connectivity of iron pnictide wires and tapes has been markedly
improved by employing Ag or Pb as dopants. At present, critical current
densities in excess of 3750 A/cm^2 (Ic = 37.5 A) at 4.2 K have been achieved on
Ag-sheathed SrKFeAs wires prepared with the above techniques, which is the
highest in iron-based wires and tapes so far. Moreover, Ag-sheathed Sm-1111
superconducting tapes were successfully prepared by PIT method at temperatures
as low as 900C, instead of commonly used temperatures of 1200C. These results
demonstrate the feasibility of producing superconducting pnictide composite
wires, even grain boundary properties require much more attention.Comment: 4 pages, 6 figures. Submitted to ASC2010 proceeding
Improved critical current densities in MgB2 tapes with ZrB2 doping
MgB2/Fe tapes with 2.5-15 at.% ZrB2 additions were prepared through the in
situ powder-in-tube method. Compared to the pure tape, a significant
improvement in the in-field critical current density Jc was observed, most
notably for 10 at.% doping, while the critical temperature decreased slightly.
At 4.2 K, the transport Jc for the 10 at.% doped sample increased by more than
an order of magnitude than the undoped one in magnetic fields above 9 T.
Nanoscale segregates or defects caused by the ZrB2 additions which act as
effective flux pinning centers are proposed to be the main reason for the
improved Jc field performance.Comment: 14 pages, 6 figure
Strongly Enhanced Current-Carrying Performance in MgB2 Tape Conductors by Novel C60 Doping
MgB2 is a promising superconductor for important large-scale applications for
both high field magnets and cryocooler-cooled magnet operated at temperatures
around 20 K. In this work, by utilizing C60 as a viable alternative dopant, we
demonstrate a simple and industrially scaleable rout that yields a 10-15-fold
improvement in the in-high-field current densities of MgB2 tape conductors. For
example, a Jc value higher than 4x10^4 A/cm^2 (4.2 K, 10 T), which exceeds that
for NbTi superconductor, can be realized on the C60 doped MgB2 tapes. It is
worth noting that this value is even higher than that fabricated using strict
high energy ball milling technique under Ar atmosphere. At 20 K, Hirr was about
10 T for C60 doped MgB2 tapes. A large amount of nanometer-sized precipitates
and grain boundaries were found in MgB2 matrix. The special physical and
chemical characteristic of C60, in addition to its C containing intrinsic
essence, is a key point in enhancing the superconducting performance of MgB2
tapes.Comment: 18 pages, 5 figure
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