Effect of citric acid doping on flux pinning in bulk MgB2 prepared by chemical solution route

In this paper, we study the doping effect of citric acid (C<inf>6</inf>H<inf>8</inf>O<inf>7</inf>), from 0 to 30 wt% of the total MgB<inf>2</inf>, on the properties, such as critical temperature (T<inf>c</inf>), critical current density (J<inf>c</inf>), irreversibility field (H<inf>irr</inf>) and crystalline structure of MgB<inf>2</inf> superconductors. The XRD patterns of samples show a slightly decrease in the a-axis lattice parameter for doped MgB<inf>2</inf>, due to the partial substitution of carbon at boron site. At 10 K the citric acid doped sample exhibits the J<inf>c</inf> values greater than 3.4×10<sup>5</sup> A/cm<sup>2</sup> in self-field, which is similar to the pure one while in high field region the J<inf>c</inf> was increased by an order of magnitude in comparison to undoped one. For MgB<inf>2</inf> doped with 15 wt% citric acid, J<inf>c</inf> still remains about 10<sup>3</sup> A/cm<sup>2</sup> in 7 T at 10 K. In addition, the self-field J<inf>c</inf> of citric acid doped sample is slightly reduced at additive level higher than 10 %. The improved flux pinning behavior could easily be seen from reduced flux pinning force curves.

[1]  Doping and effect of nano-diamond and carbon-nanotubes on flux pinning properties of MgB2 , 2007 .

[2]  S. Dou,et al.  Effect of the processing parameters of MgB1.8(SiC)0.1/Fe tapes on the critical current density , 2003 .

[3]  S. Dou,et al.  Systematic study of a MgB2+C4H6O5 superconductor prepared by the chemical solution route , 2007 .

[4]  Universal relationship between crystallinity and irreversibility field of MgB2 , 2005, cond-mat/0505008.

[5]  Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering , 2003, cond-mat/0305474.

[6]  K. Kishio,et al.  Effects of B4C doping on critical current properties of MgB2 superconductor , 2005 .

[7]  D. Wexler,et al.  Sugar as an optimal carbon source for the enhanced performance of MgB2 superconductors at high magnetic fields , 2007 .

[8]  M. Koss,et al.  Systematic study of L , 2003 .

[9]  K. Watanabe,et al.  Influence of oxygen contents of carbohydrate dopants on connectivity and critical current density in MgB2 tapes , 2007 .

[10]  Australia.,et al.  Enhancement of the critical current density and flux pinning of MgB2 superconductor by nanoparticle SiC doping , 2002, cond-mat/0207223.

[11]  R. Cava,et al.  Strongly linked current flow in polycrystalline forms of the superconductor MgB2 , 2001, Nature.

[12]  S. Dou,et al.  Enhancement of flux pinning in a MgB2 superconductor doped with tartaric acid , 2006 .

[13]  K. Watanabe,et al.  Strongly enhanced critical current density in MgB2/Fe tapes by stearic acid and stearate doping , 2007 .

[14]  Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors , 2002, cond-mat/0212129.

[15]  H. Sosiati,et al.  MgB2 films with very high critical current densities due to strong grain boundary pinning , 2004 .

[16]  P. Munroe,et al.  Comparison between nano-diamond and carbon nanotube doping effects on critical current density and flux pinning in MgB2 , 2007 .

[17]  J. Nagamatsu,et al.  Superconductivity at 39 K in Magnesium Diboride. , 2001 .

[18]  D. Larbalestier,et al.  Inter- and intragranular nanostructure and possible spinodal decomposition in low-resistivity bulk MgB_2 with varying critical fields , 2004 .