Effect of nano-SiC and nano-si doping on critical current density of MgB2 (original) (raw)
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Applied Physics Letters, 2002
Doping of MgB 2 by nano-SiC and its potential for improvement of flux pinning was studied for MgB 2-x (SiC) x/2 with x = 0, 0.2 and 0.3 and a 10wt% nano-SiC doped MgB 2 samples. Co-substitution of B by Si and C counterbalanced the effects of singleelement doping, decreasing T c by only 1.5K, introducing pinning centres effective at high fields and temperatures and enhancing J c and H irr significantly. Compared to the non-doped sample, J c for the 10wt% doped sample increased by a factor of 32 at 5K and 8T, 42 at 20K and 5T, and 14 at 30K and 2T. At 20K, which is considered to be a benchmark operating temperature for MgB 2 , the best J c for the doped sample was 2.4x10 5 A/cm 2 at 2T, which is comparable to J c of the best Ag/Bi-2223 tapes. At 20K and 4T, J c was 36,000A/cm 2 , which was twice as high as for the best MgB 2 thin films and an order of magnitude higher than for the best Fe/MgB 2 tapes. Because of such high performance, it is anticipated that the future MgB 2 conductors will be made using the formula of MgB x Si y C z instead of the pure MgB 2 .
IEEE Transactions on Appiled Superconductivity, 2003
This article was originally published as: Soltanian, S, Wang, X, Horvat, J et al, Effect of grain size and doping level of SiC on the superconductivity and critical current density in MgB/sub 2/ superconductor, IEEE Transactions on Applied Superconductivity, June 2003, 13(2)3, 3273-3276. Abstract-SiC doped MgB 2 polycrystalline samples were fabricated by in-situ reaction using different grain sizes (20 nm, 100 nm, and 37 m) of SiC and different doping levels (0, 8, 10, 12, 15 wt%). Phases, microstructures, superconductivity, critical current density and flux pinning have been systematically investigated using XRD, SEM, TEM, and magnetic measurements. Results show that grain sizes of the starting precursors of SiC have a strong effect on the critical current density and its field dependence. The smaller the SiC grains are, the better the field performance is. Significant enhancement of and the irreversibility field H irr were revealed for all the SiC doped MgB 2 with additions up to 15 wt%. A as high as 20,000 A/cm 2 in 8 Tesla at 5 K was achieved for the sample doped with 10 wt% SiC with a grain size of 20 nm. Results indicate that the nano-inclusions and substitution inside MgB 2 are responsible for the enhancement of flux pinning.
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.
The effect of Ti3SiC2 doping on the microstructure and superconducting properties of MgB2
Physics Procedia, 2012
Doping of MgB 2 by Ti 3 SiC 2 and its potential for improving the flux pinning were studied for MgB 2(1-x) (Ti 3 SiC 2 ) x with x = 0, 0.025, 0.05, 0.075 and 0.1, respectively. These bulks were pressed at 20 -50 MPa and heated to 650 -950 for 1.5 -3 h. It was found that optimal samples were obtained, which were pressed at 40 MPa and sintered at 850 for 2 h. The transition temperature (T c ) was measured on the optimal series samples using dc susceptibility and a reduction of T c from 38 K to 36 K was observed. The critical current density (J c ) which was deduced from the hysteresis loop was found to increase at doping levels x = 0.025 -0.075. With a higher doping level x = 0.1, J c was suppressed lower than that in the pure one due to non-superconducting precipitates collection at the grain boundaries.
The effect of nanoscale Fe doping on the superconducting properties of MgB 2
Superconductor Science and Technology, 2005
Iron is an important sheath material for fabrication of MgB 2 wires. However, the effect of Fe doping on the superconducting properties of MgB 2 remains controversial. In this work, we present results of nanoscale Fe particle doping in to MgB 2 . The Fe doping experiments were performed using both bulk and thin film form. It was found that Fe doping did not affect the lattice parameters of MgB 2 , as evidenced by the lack of change in the XRD peak positions for MgB 2 . Because of the high reactivity of nano-scale Fe particles, Fe doping is largely in the form of FeB at low doping level while Fe 2 B was detected at 10wt% doping by both XRD and TEM. There is no evidence for Fe substitution for Mg. The transition temperature decreased modestly with increasing Fe doping levels. The J c (H) performance was severely depressed at above 3wt% doping level. The detrimental effect of nano-scale Fe doping on both T c and J c (H) is attributable to the grain decoupling as a result of magnetic scattering of Fe-containing dopants at grain boundaries.
Flux Pinning and Superconducting Properties of Bulk MgB 2 with MgB 4 Addition
Advanced Engineering Materials
The improved performance of bulk MgB 2 material with added nanometer-sized MgB 4 particles is presented. Bulk polycrystalline MgB 2 samples with varying amount of MgB 4 x (x ¼ 0, 1, 2, 3, 4, 5, and 10 wt%) are fabricated by solid-state sintering at 775 C for 3 h in pure argon gas. Microstructural studies indicate formation of nanometer-sized grains when MgB 4 is added. Density of nanograins is inversely proportional to the MgB 4 content. The MgB 2 sample with 1 wt% of MgB 4 shows the best performance, with its self-field critical current density reaching 385 and 315 kAcm À2 at 15 and 20 K, respectively. Flux pinning diagrams reveal the domination of grain boundary pinning mechanism.
Physics Procedia, 2012
In the present work it is described the production of MgB 2 samples by using the mixture of MgB 2 with other diborides, (TaB 2 , VB 2 , and AlB 2) which have the same C32 hexagonal structure as the MgB 2 , and simultaneous addition with the diborides and SiC, that contribute with C, to replace B in the crystalline structure of the matrix. As an important result, the critical current density (J c) was improved at low magnetic fields when just the diborides are added. However, when SiC is added simultaneously with the diborides, the result is the improvement of J c at high fields. The critical temperature (T c) was maintained high.
Effect of La doping on microstructure and critical current density of MgB2
Superconductor Science and Technology, 2005
In the present study, La-doped MgB 2 superconductors with different doping level (Mg 1-x La x B 2 ; x=0.00, 0.01, 0.03 & 0.05) have been synthesized by solid-state reaction route at ambient pressure. Effect of La doping have been investigated in relation to microstructural characteristics and superconducting properties, particularly intragrain critical current density (J c). The microstructural characteristics of the as synthesized Mg(La)B 2 compounds were studied employing transmission electron microscopic (TEM) technique. The TEM investigations reveal inclusion of LaB 6 nanoparticles within the MgB 2 grains which provide effective flux pinning centres. The evaluation of intragrain J c through magnetic measurements on the fine powdered version of the as synthesized samples reveal that J c of the samples change significantly with the doping level. The optimum result on J c is obtained for Mg 0.97 La 0.03 B 2 at 5K, the J c reaches ~1.4x10 7 A/cm 2 in self field, ~2.1 x 10 6 A/cm 2 at 1T, ~2.5 x 10 5 A/cm 2 at 2.5T and ~1.8 x 10 4 A/cm 2 at 4.5T. The highest value of intragrain J c in Mg 0.97 La 0.03 B 2 superconductor has been attributed to the inclusion of LaB 6 nanoparticles which are capable of providing effective flux pinning centres.
Discovery of the new superconductor MgB_2 and its recent development
2002
We recently discovered that the intermetallic compound magnesium diboride (MgB2) exhibits the highest superconducting transition temperature (Tc = 39 K) of all metallic superconductors. In this paper we report on the basic superconducting characteristics of MgB2 and the current status of the search for applications for this material. In particular, we summarize the research into its critical current (Jc) and critical magnetic field (Hc), which are important parameters for practical applications of this material.