Systematic study of a MgB₂+C₄H₆O₅superconductor prepared by the chemical solution route

Abstract

We evaluated the additive effects of malic acid (C 4 H 6 O 5 ), from 0 to 30 wt% of the total MgB 2 , on the lattice parameters, lattice strain, amount of carbon (C) substitution, microstructures, weight fraction of MgO, critical temperature (T c ), critical current density (J c ), and irreversibility field (H irr ) of a MgB 2 superconductor. The calculated lattice parameters show a large decrease in the a-axis lattice parameter for MgB 2 + C 4 H 6 O 5 samples from 3.0861(6) to 3.0736(1) Å, with even a 10 wt% addition. This is an indication of C substitution into boron sites, with the C coming from C 4 H 6 O 5 , resulting in enhancement of J c and H irr . Specifically, the H irr of the MgB 2 + C 4 H 6 O 5 samples prepared by the chemical solution route reached around 7 T at 20 K, with a T c reduction of only 1.5 K. In addition, the self-field J c of the MgB 2 + C 4 H 6 O 5 samples was only slightly reduced at an additive level as high as 30 wt%. However, residual oxygen after evaporation processing contributed to a large amount of MgO in our MgB 2 + 30 wt% C 4 H 6 O 5 samples. These problems can be further controlled by the amount of C 4 H 6 O 5 additive or different evaporation temperatures.

Strong competition between the δl and δTc flux pinning mechanisms in MgB2 doped with carbon containing compounds

“…21 The critical temperature T c was defined as the onset temperature at which diamagnetic properties were observed. This temperature was 35Ϯ 0.20 K for the both samples.…”

Enhanced critical parameters of nanocarbon doped MgB2 superconductor

“…Thus, it enhances the critical parameters both ways and results in superior results than through other dopants. [13][14][15] Substantial increment is noticed in the H c2 ͑0͒ value for the nanocarbon doped samples as compared to pristine MgB 2 on applying suitable theoretical model. The quantitative description is given in Sec.…”

“…[13][14][15] Thus, along with MgB 2 , the nanocarbon doped samples are also taken into consideration. The critical parameters such as H c2 , H irr , and J c enhance significantly by nanocarbon substitution at boron site.…”

Influence of disorder on the in-field Jc of MgB2 wires using highly active pyrene

“…In addition, although we conducted evaporation processing to eliminate the oxygen ͑O͒ content, the fraction of MgO due to included O from the carbohydrate increased gradually with increasing doping level. 12 If we can reduce the MgO fraction within the matrix and find a highly active C source that will be effective at lower sintering temperatures 600°C, the same as for MgB 2 formation, we speculate that the resulting high disorder due to C substitution, as well as strong flux pinning due to the small crystalline size, can have simultaneous positive effects on the infield J c . A higher sintering temperature is usually necessary for most of the other C sources, leading to crystalline growth and worse pinning.…”