Improved superconducting properties in nanocrystalline bulk MgB2

Gümbel, A.; Eckert, J.; Fuchs, G.; Nenkov, K.; Müller, K.‐H.; Schultz, L.

doi:10.1063/1.1469654

Cited by 219 publications

(147 citation statements)

References 13 publications

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“…A ball milling process was adopted to further enhance the uniformity. [23][24][25] The mixed un-reacted powders were put into a metallic tube and then heat treated. The field dependence of the critical current measured by the standard four-probe method is shown in Figure 1a.…”

Section: Resultsmentioning

confidence: 99%

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

et al. 2012

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Increasing dissipation-free supercurrent has been the primary issue for practical application of superconducting wires. For magnesium diboride, MgB 2 , carbon is known to be the most effective dopant to enhance high-field properties. However, the critical role of carbon remains elusive, and also low-field critical current density has not been improved. Here, we have undertaken malic acid doping of MgB 2 and find that the microscopic origin for the enhancement of high-field properties is due to boron vacancies and associated stacking faults, as observed by high-resolution transmission electron microscopy and electron energy loss spectroscopy. The carbon from the malic acid almost uniformly encapsulates boron, preventing boron agglomeration and reducing porosity, as observed by three-dimensional X-ray tomography. The critical current density either exceeds or matches that of niobium titanium at 4.2 K. Our findings provide atomic-level insights, which could pave the way to further enhancement of the critical current density of MgB 2 up to the theoretical limit.

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Section: Resultsmentioning

confidence: 99%

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

et al. 2012

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“…4 There have also been reports from other groups using different ball-milling systems. For example, Gümbel et al 5 attempted to fabricate nanostructured MgB 2 by mechanical alloying of elemental Mg and amorphous B powders in a planetary ball mill, followed by hot pressing at about 700°C. They achieved a critical current density of J c ϳ 1 ϫ 10 5 A cm −2 at an applied field of 2.1 T and 20 K. Fang et al 6 fabricated superconducting iron-clad MgB 2 tapes via the standard PIT process, using an ultrafine Mg and B mixture precursor prepared by high-energy ball milling.…”

Section: Introductionmentioning

confidence: 99%

Phase transformation and superconducting properties of MgB2 using ball-milled low purity boron

Kim

Hossain

et al. 2008

Journal of Applied Physics

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MgB 2 samples were prepared by using 96% boron (B) powder with strong crystalline phase that had been ball milled for various times. We observed samples that contained ball-milled 96% B in comparison with one made from as-supplied commercial 96% B, with the results showing a significant enhancement in the high field critical current density (Jc) due to small grain size and better reactivity. Specifically, many grain boundaries for MgB2 could be acting as strong flux pinning centers. Based on Rowell connectivity analysis, when the ball-milling time increased, the connectivity factor, described as the active cross-sectional area fraction (AF), was decreased. This implies that the intergrain connectivity became worse. These properties could lead to poor Jc in low field. However, the pinning force strength, Jc1/2×B1/4, of samples using ball-milled 96% B is larger than that of the reference sample using commercial 96% B powder. These results accompany enhanced irreversibility (Hirr) and upper critical fields (Hc2).

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“…Several techniques, such as alloying [11,12,13], particle irradiation [14,15,16,17] and mechanical processing [9,18] have been employed in order to improve the flux-pinning in MgB 2 , but with limited success. In particular, proton irradiation [14] increased B irr at 20 K, but also suppressed low-field J c , whereas alloying seems to enhance J c , but has little effect on B irr [12,13].…”

Section: Introductionmentioning

confidence: 99%

Correlated vortex pinning in Si-nanoparticle doped MgB2

Kušević

Babić

Husnjak

et al. 2004

Solid State Communications

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The magnetoresistivity and critical current density of well characterized Si-nanoparticle doped and undoped Cu-sheathed MgB2 tapes have been measured at temperatures T ≥ 28 K in magnetic fields B ≤ 0.9 T. The irreversibility line Birr(T ) for doped tape shows a stepwise variation with a kink around 0.3 T. Such Birr(T ) variation is typical for high-temperature superconductors with columnar defects (a kink occurs near the matching field B φ ) and is very different from a smooth Birr(T ) variation in undoped MgB2 samples. The microstructure studies of nanoparticle doped MgB2 samples show uniformly dispersed nanoprecipitates, which probably act as a correlated disorder. The observed difference between the field variations of the critical current density and pinning force density of the doped and undoped tape supports the above findings.

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Improved superconducting properties in nanocrystalline bulk MgB2

Cited by 219 publications

References 13 publications

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

Phase transformation and superconducting properties of MgB2 using ball-milled low purity boron

Correlated vortex pinning in Si-nanoparticle doped MgB2

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