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Abstract: In the past 5 years, various kinds of doping of MgB2, including single elements (metal and non-metal), silicates, various carbon sources, and other compounds have been investigated and reported. Most nanoparticle doping leads to improvement of critical current density, J c(H), and performance, but some types show a negative effect. In this paper, the effect of carbon doping on J c and the upper critical field, H c2, of MgB2 is reviewed. Carbon substitution effects make two distinguishable contributions to the enhancement of J c field performance: increase of H c2 and improvement of flux pinning, both because carbon substitutes for boron in the MgB2 lattice. Among all the carbon sources so far, nano-SiC has been confirmed to be the most effective dopant to enhance the J c in magnetic fields and H c2. An irreversibility field, H irr, of 10T has been achieved with nano-SiC doping at 20K, exceeding H irr of NbTi at 4.2K. Besides that, H c2 of carbon alloyed MgB2 film has reached the value of 71T. The significant enhancement in J c(H) and H c2 via carbon substitution has provided great potential for practical applications of MgB2. The dual reaction model proposed by the authors’ group provides a comprehensive understanding of the mechanism of enhancement in J c and H c2 by chemical doping. Further improvement in self-field J c performance while maintaining the already achieved in-field performance remains as a major challenge in the development of MgB2. [Copyright &y& Elsevier]

Abstract: We studied the effects of MgB2 with embedded multiwall carbon nanotubes (MWCNTs) on the crystallinity, lattice parameters, critical current density (J c), upper critical field (H c2), irreversibility field (H irr), and microstructure of MgB2. Fe sheathed un-doped and MWCNT doped MgB2 wires were fabricated by the powder-in-tube (PIT) method and sintered at the high sintering temperatures of 900°C. We observed that for the MWCNT doped sample high temperature sintering resulted in depressed crystallinity, shrinkage of the a-lattice parameter, higher J c up to 12T, and lower critical temperature (T c) values. Specifically, MWCNT doped samples sintered at 900°C exhibited excellent J c, ∼104 Acm−2 up to 9T at 4.2K. This can be explained by lattice distortion and poor crystallinity due to carbon (C) substitution from the MWCNT. [Copyright &y& Elsevier]

Abstract: Single grain, Ag-doped Y–Ba–Cu–O bulk superconductors of up to 30mm in diameter have been fabricated successfully by a seeded infiltration and growth (IG) technique. These samples exhibit low porosity compared with samples grown by conventional top seeded melt growth (TSMG). The density of voids within as-processed IG samples can be reduced further by adding metallic Ag, rather than Ag2O, to the Y2BaCuO5 (Y-211) pre-form. An inhomogeneous distribution of Y-211 has been observed in these samples. Finally, a maximum trapped magnetic field of 0.5T was observed for Ag-doped Y–Ba–Cu–O of diameter 30 mm at liquid nitrogen temperature (77K). [Copyright &y& Elsevier]

Abstract: In order to study the influence of the amorphous Boron powder on the superconducting properties, MgB2 bulk samples were prepared using 96% and 99% pure commercial Boron powder as well as 92% commercial Boron powder after purification process. The results showed that the original 96% and the purified 92% powders have larger particle size compared to the pure 99% Boron powder, which leads to reduce magnetic critical current densities. In order to get higher performance MgB2, the purified low grade Boron powder need further control of their microstructure such as smaller particle size to enhance flux pinning from the grain boundaries which represent effective pinning centers. [Copyright &y& Elsevier]