Enhancing the superconducting temperature of MgB2 by SWCNT dilution (original) (raw)
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SiC and carbon nanotube distinctive effects on the superconducting properties of bulk MgB2
Journal of Applied Physics, 2008
This work describes in detail the simultaneous enhancement of the upper critical field (Hc2) and the critical current density (Jc) of MgB2 bulk samples doped with nano-SiC particles, as well as single-walled and double-walled (dw) carbon nanotubes (CNTs). The magnetization properties were examined in a superconducting quantum interference device magnetometer, and four-probe transport measurements were performed using a 50T pulsed magnet to determine Hc2(T ). We found that the Jc enhancement is similar in all doped samples at 5K but nano-SiC addition is more effective to improve the flux pinning in the high temperature range (T⩾20K); this improvement cannot solely be attributed to the C incorporation to the lattice but also to the presence of other types of defects (i.e., several kinds of nanoinclusions). CNTs produce a better C incorporation that is more effective to enhance Hc2 [i.e., dwCNT-doped samples reached a record Hc2(0)˜44T value for bulk MgB2]. All the Hc2(T ) curves obtained for different types of doping can be successfully described using a model for a two-gap superconductor in the dirty limit.
EUREKA: Physics and Engineering
MgB2/CNT is a promising candidate for superconducting wire application due to its excellent mechanical properties and carbon nanotube’s low density. However, strong interfacial adhesion between the CNT reinforcement and the MgB2 matrix is difficult to manage. Therefore, this study examines the synthesis and characterization of magnesium diboride (MgB2) superconductors with carbon nanotubes (CNTs) and tin (Sn) addition. Determining the proper method and combination of CNT & Sn affects MgB2 superconductors is crucial. Raw materials of magnesium (Mg), boron (B), Sn, and multi-walled carbon nanotubes (MWCNTs) were used for a solid-state reaction process to determine the proper synthesis method and the effect of CNT on superconductors’ critical temperature. Each sample was obtained by weighing the raw material first, followed by hand grinding with agate mortars for 3 hours. The pelletization was then conducted by using a compact pressing machine with a pressure of 350 MPa. The compacted ...
Enhanced Tc in MgB2 by SWCNT Dilution
We report for the first time a nonsubstitutional hole-doping of the MgB2 structure and an increase in Tc by SWCNT dilution. The SWCNT concentration was varied from 0.05wt% to 5wt%. We investigated the temperature dependence resistivity from 10K to 300K of sintered MgB2 powder containing dilute amount of ultra-high purity single wall carbon nanotubes. Micro-Raman spectroscopy, field emission scanning electron microscope and x-ray diffraction were used to analyze the interfacial interactions between the carbon nanotubes and the magnesium diboride grains. We obtained an increase in Tc from 41.1K to 45.8K. This is attributed charge transfer: electron transfer from the MgB2 structure to the SWCNT structure. This consequently leads to hole-doping of the MgB2 structure and the enhancement we see in Tc. This is confirmed by micro-Raman analysis of the phonon states of the SWCNT in the composites. This is explained in terms of the interplay between impurity scattering and hole-doping. This r...
2020
The result of adding carbon nanotubes (CNTs) to the lattice parameters, critical temperature and electrical resistivity of the MgB 2 superconductors is reported. Structurally, the addition of CNTs was found to decrease the a -lattice from 3.086 A of CNTs free sample to 3.078 A and 3.074 A of 5% and 10% CNTs added samples due to a substitution of C at the B site which presence in the form of Mg(B 1-x C x ) 2 main phase. The doping level x of CNTs added samples were 2.25 at% and 3.75 at% respectively. The unreacted CNTs presence as the second phase and further acting as the suppression agent for crystallite growth. The addition of CNTs is also to refine the grain size and improves the grain connectivity. Samples show a metallic behavior which observed only at temperatures above ~41 K, below which, a sharp transition of resistivity occurred toward zero resistivity, confirming the superconductivity behavior. This study concluded that the effect of CNTs addition affects the structural pa...
Carbon solubility and superconductivity in MgB 2
Physica C-superconductivity and Its Applications, 2002
Successful replacement of B by C in the series MgB 2-x C x for values of x upto 0.3 are reported. Resistivity and ac susceptibility measurements have been carried out in the samples. Solubility of carbon, inferred from the observed change in the lattice parameter with carbon content indicates that carbon substitutes upto x=0.30 into the MgB 2 lattice. The superconducting transition temperature, T C measured both by zero resistivity and the onset of the diamagnetic signal shows a systematic decrease with increase in carbon content upto x=0.30, beyond which the volume fraction decreases drastically. The temperature dependence of resistivity in the normal state fits to the Bloch-Gruneisen formula for all the carbon compositions studied. The Debye temperatures, θ D , extracted from the fit is seen to decrease with carbon content from 900K to 525K, whereas the electron-phonon interaction parameter, λ, obtained from the McMillan equation using the measured T C and θ D , is seen to increase monotonically from 0.8 in MgB 2 to 0.9 in the x=0.50 sample. The ratio of the resistivities between 300K and 40K versus T C is seen to follow the Testardi correlation for the C substituted samples. The decrease in T C is argued to mainly arise due to large decrease in θ D with C concentration and a decrease in the hole density of states at N(E F ).
Effect of carbon-doping in bulk superconducting MgB2 samples
Physica C: Superconductivity, 2001
Bulk superconducting samples of MgB 2 were prepared by solid state reaction of stoichiometric quantities of Mg turnings and B in a sealed Ta cylinder at 890 ºC for 2 hours. The "as-synthesized" MgB 2 samples had a T c of 39 K, as defined as the onset of diamagnetism. The crystal symmetry was found to be hexagonal with lattice parameters, a=3.0856 Å, and c=3.5199 Å, similar to the literature values. To study the effect of carbon doping in MgB 2 , various C-containing samples of x varying from 0 to 1.00 in MgB 2-x C x were prepared. Magnetic characterizations indicate that the T c onset is same for pure and C-doped samples for x = 0.05, and 0.10. However, the shielding signal decreased monotonically with C content, apparently due to the presence of carbon on the grain boundaries that isolates grains and prevents flow of supercurrents on the perimeter.