B J Senkowicz et al 2007 Supercond. Sci. Technol. 20 650 doi:10.1088/0953-2048/20/7/011
B J Senkowicz1,2, A Polyanskii2, R J Mungall1, Y Zhu1, J E Giencke1, P M Voyles1, C B Eom1, E E Hellstrom1 and D C Larbalestier2
Show affiliationsWe have systematically doped pre-reacted MgB2 with C by high-energy ball milling, and obtained peak Jc (8 T, 4.2 K)>500 A mm−2 in a form compatible with powder-in-tube wire manufacture. Effects of carbon doping by this method were qualitatively similar to single crystals and CVD (chemical-vapour-deposited) filaments, but Tc, Hc2, and resistivity measurements indicate more electron scattering than in single crystals and CVD filaments of similar composition. We attribute both the high Jc(H) and the large degree of electron scattering to the high grain boundary density associated with our very fine ~50 nm grain size. At high C concentrations (C/(B+C)>0.07) Jc fell sharply. We identified the cause of the Jc decline to be a sharp decline in connectivity. This work demonstrates how Jc(H) of pre-reacted MgB2 can be improved by simultaneously alloying with C and refining grains through cold work and further improvement of connectivity.
74.62.Dh Effects of crystal defects, doping and substitution
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
Issue 7 (July 2007)
Received 20 March 2007, in final form 30 April 2007
Published 4 June 2007
B J Senkowicz et al 2007 Supercond. Sci. Technol. 20 650
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