The effects of C substitution and disorder on the field dependent critical current density in MgB2 with nano-SiC additions

Abstract

In this work, nano sized SiC powders were mixed with Mg and B and reacted by either a onestep insitu or two-step method resulted in different level of C substitution. X-ray diffraction shows the presence of Mg2Si signifying that the reaction between SiC and Mg occurred leading to the release of C in samples reacted in one-step method. Moreover, the much reduced value of a-axis indicates C substitution took place. Resistivity measurements showed higher intragrain scattering owing to a higher density of defects and/or impurities. These samples also show higher Hirr and Hc2 at 20 K in comparison to samples with mainly unreacted SiC (hence lower C substitution). More importantly, their Jc's are more insensitive to high magnetic field (>4 T) at 6 K. However, at 20 K the effect of C content on Jc(H) is less pronounced. Finally, the order of magnitude of Jc(H) at both 6 K and 20 K is rather dominated by pinning.

EDX and ion beam treatment studies of filamentary in situ MgB2 wires with Ti barrier

“…1a. For improvement of in-field critical current density 5 wt% of SiC was added into a mixture of Mg and B powders [9,10]. Cold drawing deformation was applied from the composite wire diameters between 0.860 mm and 0.375 mm [8].…”

“…The later silicon-rich layer originates in process of decomposition of SiC, which was used as a dopant in MgB 2 filaments. We suppose that during the heat treatment the carbon from decomposed SiC was built-in MgB 2 lattice [9][10][11] and Si originally spread over the whole Mg-B filament (see Figs. 2b and 3a) was gettered by titanium barrier out off the MgB 2 .…”

“…Thus increased Si content in the filament can result in a larger volume of non-superconducting secondary phase and in the same time decrease of Mg/B ratio. The presence of Si accumulated at grain boundaries can worsen substantially inter-grain connectivity, too [10].…”

Micro-indentation study of Mg-addition MgB2 superconducting wires

“…Since the discovery of superconductivity in MgB 2 [1], many efforts have been made to improve the properties of MgB 2 by doping and/or adding and changing conditions of sample preparation [2][3][4][5][6]. The improvement of the superconducting properties of the sample is a decisive goal to enable its potential application.…”