In situsynthesis and current-carrying characteristics of superconducting MgB₂–B₄C composites with MgB₂fractions ranging from 18% to 85%

Abstract

Carbon is known to be the most effective dopant to enhance the high-field current-carrying capacity for high-power applications of MgB2 superconductors. Using B4C instead of B to synthesize MgB2 will be expected to produce superconducting MgB2 together with in situ carbon doping. By using just two reaction substances, B4C and Mg, superconducting MgB2–B4C composites with MgB2 fractions ranging from 18 to 85% were fabricated successfully by solid-state reaction. The influence of the grain size of the B4C raw material on the critical current density (Jc), the fraction of MgB2, and the critical transition temperature (Tc) of MgB2–B4C composites were investigated. Tc, Jc, and the fraction of MgB2 were increased with decrease in the grain size of the B4C raw material. Compared with a pure MgB2 superconductor, the critical transition temperature of the MgB2 composites fabricated with small B4C grain size was suppressed slightly, but the in-field current-carrying capacity was improved significantly. By using B4C raw material with a grain size of 2.5 μm, the resultant superconducting composite showed a critical transition temperature of 33.0 K, a high self-field Jc of 0.7 × 106 A cm−2, and a remarkable in-field current density value of 1 × 104 A cm−2 under 6 T at 10 K. These results indicate that the composites can be applied directly in high-power applications of superconductors. The enhancement of flux pinning in the superconducting MgB2–B4C composite is discussed and considered to be mainly due to the increment in the effective surface area of grain boundaries per unit volume.

Effect of deformation with Bridgman anvils on the structure, hardness, and critical current of a massive MgB2-based sample

“…In such a structure of the sample, a decrease in the volume frac tion of contacts between superconducting MgB 2 areas should be expected. This result agrees with data of [12], in which it was shown that T c and j c of the super conducting MgB 2 -B 4 C composite depend on the MgB 2 phase fraction. The critical current density of the initial sample (sample no.…”

Nanostructural inhomogeneities acting as pinning centers in bulk MgB2with low and enhanced grain connectivity

“…Any kind of disorder potentially changes the properties of MgB 2 . Disorder can be introduced in a controlled way by doping [1][2][3][4][5][6][7][8][9] or irradiation [10,11], but often arises from the preparation conditions [12,13] and generally decreases the transition temperature [1].…”

“…A positive effect in enhancing the critical currents of MgB 2 is played, for example, by dopants, such as silicon carbide, carbon (carbon nanotubes, nanodiamonds) or carbon sources (ethyltoluene, carbohydrates, sugar, maleic acid, maleic anhydride, paraffin, boron carbide, toluene, acetone, ethanol, tartaric acid, etc), TiC, CaB 6 , Ti, Zr, ZrB 2 [1][2][3][4][5][6][7][8][9]. In their review, Collings et al [1] concluded that the introduction of dopants can have one or more effects, which may result in an increase in the bulk pinning strength: (1) by increasing the crystal's H c2 and H irr , (2) by forming a wide distribution of point pinning centers, each one being described by an elementary pinning force f p , and (3) by producing localized lattice strains, which also contribute to flux pinning.…”

Bulk MgB2 Superconducting Materials: Technology, Properties, and Applications

“…Among the dozens of studied additions to MgB 2 , the ones that are the most effective from the point of view of an increase in the critical current density are carbon, carbon-containing compounds, silicon carbide, titanium, tantalum, zirconium, and compounds containing these metals [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 ]. Relatively recently, in the literature [ …”