The doping effect of multiwall carbon nanotube on MgB2∕Fe superconductor wire

Abstract

We evaluated the doping effect of two types of multiwall carbon nanotubes ͑CNTs͒ with different aspect ratios on MgB 2 / Fe monofilament wires. Relationships between microstructure, magnetic critical current density ͑J c ͒, critical temperature ͑T c ͒, upper critical field ͑H c2 ͒, and irreversibility field ͑H irr ͒ for pure and CNT doped wires were systematically studied for sintering temperature from 650 to 1000°C. As the sintering temperature increased, T c for short CNT doped sample slightly decreased, while T c for long CNT doped sample increased. This indicates better reactivity between MgB 2 and short CNT due to its small aspect ratio, and substitution of carbon ͑C͒ from short CNT for boron ͑B͒ occurs. In addition, short CNT doped samples sintered at high temperatures of 900 and 1000°C exhibited excellent J c , and this value was approximately 10 4 A/cm 2 in fields up to 8 T at 5 K. This suggests that short CNT is a promising carbon source for MgB 2 superconductor with excellent J c . In particular, inclusion of nanosized MgO particles and substitution of C into the MgB 2 lattice could result in strong flux pinning centers.

ImprovedJcof MgB2superconductor by ball milling using different media

“…A significant enhancement in the J c of MgB 2 has been achieved through chemical doping with carbon (C) containing compounds, such SiC, C, B 4 C, and CNT. However, doping effects have been limited by the agglomeration of nanosized dopants and poor reactivity between boron (B) and C [2][3][4][5][6][7]. Moreover, the self-field and low-field J c were depressed due to the decrease in the superconducting volume.…”

Carbohydrate doping to enhance electromagnetic properties of MgB2 superconductors

“…1͒ and the high critical current density ͑J c ͒ of Ͼ10 5 cm −2 in moderate fields, magnesium diboride ͑MgB 2 ͒ superconductors could offer the promise of important largescale applications to be operated at 20 K. A significant enhancement in the electromagnetic properties of MgB 2 has been achieved through doping with various forms of carbon ͑C͒. [2][3][4][5][6] To take advantage of its T c of 39 K, enhancements of both the upper critical field ͑H c2 ͒ and J c are essential. Attempts to accomplish this have invoked the introduction of numerous techniques including chemical doping, [2][3][4][5][6] irradiation, 7 and various thermomechanical processing techniques.…”

“…[2][3][4][5][6] To take advantage of its T c of 39 K, enhancements of both the upper critical field ͑H c2 ͒ and J c are essential. Attempts to accomplish this have invoked the introduction of numerous techniques including chemical doping, [2][3][4][5][6] irradiation, 7 and various thermomechanical processing techniques. 8,9 Chemical doping is a simple and readily scalable technique.…”

“…All samples were characterized by x-ray diffraction ͑XRD͒, field emission gun-scanning electron microscopy ͑FEG-SEM͒, J c , T c , H irr , and H c2 . 3 The lattice parameters were obtained from Rietveld refinement. Table I shows the measured data for the undoped MgB 2 and MgB 2 +C 4 H 6 O 5 samples with different addition levels.…”

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

“…[1][2][3][4][5][6] From the applications point of view, the effect of C doping on the flux pinning properties and upper critical field ͑H c2 ͒ is crucially important. Recently, several groups have reported a significant improvement in critical current density ͑J c ͒, H c2 , and irreversibility field ͑H irr ͒ in MgB 2 through C doping in various forms, including C, SiC, carbon nanotube ͑CNT͒, and B 4 C. [7][8][9][10] Among various C precursors, CNTs are particularly interesting as their special geometry may induce more effective pinning centers compared to other C-containing precursors. Furthermore, CNTs have unusual electrical, mechanical, and thermal properties.…”