Alignment of Carbon Nanotube Additives for Improved Performance of Magnesium Diboride Superconductors

Dou, Shi Xue; Yeoh, Wai Kong; Shcherbakova, Olga V; Wexler, David; Liu, Ying; Ren, Zhong; Munroe, Paul; Chen, Soo Kien; Tan, K.S.; Glowacki, B.A.; MacManus‐Driscoll, Judith L.

doi:10.1002/adma.200501617

Cited by 59 publications

(44 citation statements)

References 29 publications

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“…[3][4][5][6][7][8][9][10][11] In the vast majority of these doping works the nanodopants have been introduced via a solid-state reaction; [12][13][14][15][16][17] however, an important challenge is achieving homogeneity between a small amount of nanoadditives and matrix materials, because any dry mixing poses the major problem of nanoparticle agglomeration. In this Communication, we have chosen sugar (C 6 H 12 O 6 ) as the dopant.…”

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Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB₂ with Enhanced Current‐Carrying Performance

et al. 2006

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The second boom in superconductivity during the last two decades has been powered up by the discovery of MgB 2 having the transition temperature (T c ) of 39 K [1] as well as a strong market potential for applications. The strongest impact on the development of this superconductor has been made by the discovery of the significant enhancement of the critical current density (J c ) as a function of the applied magnetic field (B a ) that results from SiC nanodoping.[2] Since then, a large variety of dopants have been attempted in order to achieve or improve on the attained enhancement. [3][4][5][6][7][8][9][10][11] In the vast majority of these doping works the nanodopants have been introduced via a solid-state reaction; [12][13][14][15][16][17] however, an important challenge is achieving homogeneity between a small amount of nanoadditives and matrix materials, because any dry mixing poses the major problem of nanoparticle agglomeration. In this Communication, we have chosen sugar (C 6 H 12 O 6 ) as the dopant. This is the most readily available carbohydrate that enables liquid homogeneous mixing. We have demonstrated that sugar doping resulted in an effective substitution of carbon for boron in MgB 2 , so that a significant enhancement of the J c performance over the entire applied field range is readily achievable. This method is applicable to the fabrication of a wide range of carbon-based compounds and composites. The MgB 2 superconductor has a strong potential for various applications because of its high T c , strong connectivity between the grains, and low anisotropy.[18] One major problem is posed by the relatively weak pinning in the pure material, which leads to rather rapid degradation of J c as a function of B a . Different approaches, such as irradiation and chemical doping, have been used to enhance the pinning strength in MgB 2 . [2,[4][5][6]10,11,17,19] . Chemical doping is a desirable, relatively easy, and cheap method to introduce pinning sites into the superconductor. Nanometer-size SiC has been found to be the most effective dopant for J c enhancement. [2,5,6,15,[20][21][22] The carbon-based materials introduce the strongest enhancement of J c (B a ) performance in MgB 2 , owing to the fact that carbon can be incorporated into the MgB 2 crystal lattice by replacing boron. This substitution results in the enhancement of chargecarrier scattering occurring on C-substituted sites and Mgvacancies in two energy bands discovered in this material. [23] This scattering has been shown to be responsible for the considerable upper critical field increase.[24] Generally, nanometer-sized particles are necessary to ensure a homogeneous doping procedure, which in our case should provide a strong enhancement of the pinning force. However, regardless of how well mixing, grinding, [2,5] milling, or ultrasonic dispersion [16] is carried out, the doping process is usually impeded by the formation of large agglomerates of particles. In addition, the precursor materials are commonly in their passivated state, which can...

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Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB₂ with Enhanced Current‐Carrying Performance

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“…11 These properties could improve the interior thermal stability, heat dissipation, and mechanical strength of MgB 2 superconductor wire. The Kim et al 8 and Dou et al 12 have demonstrated that CNT doping not only resulted in a significant enhancement of in-field J c performance but also improved heat transfer and dissipation. The CNTs are composed of one or more concentric graphene cylinders, which are called single-walled carbon nanotubes ͑SWCNTs͒ and multi-walled carbon nanotubes ͑MWCNTs͒, respectively.…”

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Enhancement of in-field Jc in MgB2∕Fe wire using single- and multiwalled carbon nanotubes

Kim

Yeoh

Qin

et al. 2006

Applied Physics Letters

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We investigated the doping effects of SWCNTs and MWCNTs on the T c , lattice parameters, J c (B), microstructure, and H c2 of MgB 2 /Fe wire. These effects systematically showed the following sequence for T c and the a-axis: the SWCNT doped wire < the MW short CNT doped wire < the MW long CNT doped wire < un-doped wire, while J c (B) followed the sequence of the SWCNT doped wire > the MW short CNT doped wire > the MW long CNT doped wire > un-doped wire. A dominating mechanism behind all these findings is the level of C substitution for B in the lattice. The best J c (B) and H c2 were obtained on SWCNT doped wire because the level of C substitution for B in this wire is higher than all others.

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“…However, the critical current density (J c ) of MgB 2 , as one of the important performance factors in superconducting applications, is suppressed rapidly in high magnetic fields due to its weak flux pinning [1,2]. The J c value has been observed to improve by addition of element or compound in MgB 2 [3][4][5][6][7][8][9][10][11][12]. The enhancement of J c is mainly due to the formation of fine grains or thin layers between grain boundaries by additions, which can act as strong flux pinning centers.…”

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Superconducting Properties and Microstructure of Nanocrystalline MgB2 Bulk Prepared by Sintering of Ball-Milled Powders

Sun

Long-hui

Song

et al. 2012

J Supercond Nov Magn

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Ultrafine nanostructured MgB 2 bulks with an average grain size less than 10 nm have been fabricated by high-energy ball milling and subsequent high pressure sintering. Microstructural evolution in MgB 2 subjected to highenergy ball milling has been investigated by means of X-ray diffraction (XRD). The finer grain size of MgB 2 powders of about 7 nm has been estimated from Rietveld refinement analysis of XRD data, which is confirmed by a transmission electron microscope (TEM) observation. There is almost no grain growth in the subsequent sintering at low temperature of 600°C under pressure of 3-5 GPa for 10-30 min. The nanocrystalline MgB 2 bulks exhibit the lower onset critical transition temperatures (T c onset ) of 32-33 K. The relative wider width of the magnetic hysteresis loops at high external magnetic field and the higher critical current density (J c ) are obtained in nanocrystalline bulks. J c is as high as 10 5 A/cm 2 in 8 T at 10 K and 2.7 × 10 3 A/cm 2 in 4 T at 20 K.Keywords MgB 2 · Nanocrystalline bulk · High pressure sintering · Magnetic hysteresis loops · Critical current density Y. Sun ( ) · L. Zhu · X. Song

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Alignment of Carbon Nanotube Additives for Improved Performance of Magnesium Diboride Superconductors

Cited by 59 publications

References 29 publications

Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB₂ with Enhanced Current‐Carrying Performance

Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB₂ with Enhanced Current‐Carrying Performance

Enhancement of in-field Jc in MgB2∕Fe wire using single- and multiwalled carbon nanotubes

Superconducting Properties and Microstructure of Nanocrystalline MgB2 Bulk Prepared by Sintering of Ball-Milled Powders

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Alignment of Carbon Nanotube Additives for Improved Performance of Magnesium Diboride Superconductors

Cited by 59 publications

References 29 publications

Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB2 with Enhanced Current‐Carrying Performance

Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB2 with Enhanced Current‐Carrying Performance

Enhancement of in-field Jc in MgB2∕Fe wire using single- and multiwalled carbon nanotubes

Superconducting Properties and Microstructure of Nanocrystalline MgB2 Bulk Prepared by Sintering of Ball-Milled Powders

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Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB₂ with Enhanced Current‐Carrying Performance

Sugar Coating of Boron Powder for Efficient Carbon Doping of MgB₂ with Enhanced Current‐Carrying Performance