Large upper critical field and irreversibility field in MgB2 wires with SiC additions

Abstract

Resistive transition measurements are reported for MgB 2 strands with SiC dopants. The starting Mg powders were 325 mesh 99.9% pure, and the B powders were amorphous, 99.9% pure, and at a typical size of 1-2 µm. The SiC was added as 10 mol% of SiC to 90 mol% of binary MgB 2 [(MgB2)0.9(SiC)0.1]. Three different SiC powders were used; the average particle sizes were 200 nm, 30 nm, and 15 nm. The strands were heat treated for times ranging from 5 to 30 minutes at temperatures from 675°C to 1000°C. Strands with 200 nm size SiC additions had µ 0 H irr and B c2 which maximized at 25.4 T and 29.7 T after heating at 800°C for 30 minutes. The highest values were seen for a strand with 15 nm SiC heated at 725°C for 30 minutes which had a µ 0 H irr of 29 T and a B c2 higher than 33 T.

Carbohydrate doping to enhance electromagnetic properties of MgB2 superconductors

“…2 These record high properties have been confirmed and reproduced by many groups, 2,5,10,11 and the performance records remain unbroken up to now. However, the best high-field J c values achieved in the SiC doped MgB 2 wires were compromised by the reduction in self-field and low-field J c .…”

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

“…The field dependence of the critical current measured by the standard four-probe method is shown in Figure 1a. Compared with other types of carbon doping, such as SiC doping, [26][27][28][29] the malic acid-doped sample studied in this work not only shows increased high-field critical current density, but also increased low-field critical current density, even comparable to that of NbTi, exceeding 10 5 A cm À2 at 4.2 K and 6 T. At higher temperature, for example at 20 K, the critical current density of SiC-doped samples has been reported to be decreased compared with the un-doped samples, but here, even at 20 K, the critical current density was increased.…”

Influence of the upper critical-field anisotropy on the transport properties of polycrystalline MgB2

“…It is well documented that B c2 can be enhanced significantly by various techniques [1,2,3,4,5,6,7,8,9,10,11]. Although the mechanisms involved in these changes are not yet fully understood, impurity scattering in both bands seems to play a major role.…”

“…In MgB 2 thermal effects should play only a minor role due to its comparatively low Ginzburg number. Nevertheless, the critical currents become too small for power applications at fields well below H c2 , even at 4.2 K. Fortunately, the upper critical field of MgB 2 can be rather easily enhanced by certain preparation conditions [1,2,3], doping [4,5,6,7,8] or irradiation [9,10,11], and exceeds 30 T (at 0 K). Even for such "high-H c2 " materials, the application range is limited to around 10 T in polycrystalline samples.…”