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High performance Cu doped MgB 2 bulks were prepared by an in-situ method with carbon-coated amorphous boron as precursor. It was found that the usage of carbon-coated boron in present work leads to the formation of uniformly refined MgB 2 grains, as well as a high level of homogeneous carbon doping in the MgB 2 samples, which significantly enhance the J c in both Cu doped and undoped bulks compared to MgB 2 bulks with normal amorphous boron precursor. Moreover, minor Cu can service as activator, and thus facilitates the growth of MgB 2 grains and improves crystallinity and grain connectivity, which can bring about the excellent critical current density ( J c ) at self fields and low fields (the best values are 7 × 10 5 A/cm 2 at self fields, and 1 × 10 5 A/cm 2 at 2 T, 20 K, respectively). Simultaneously, minor Cu addition can reduce the amount of MgO impurity significantly, also contributing to the improvement of J c at low fields. Our work suggests that Cu-activated sintering combined with employment of carbon-coated amorphous boron as precursor could be a promising technique to produce practical MgB 2 bulks or wires with excellent J c on an industrial scale. [ABSTRACT FROM AUTHOR]

As the “low activation” superconductor, Mg 11 B 2 has a potential application in superconducting coils for fusion reactor. In present work, the sintering process and critical current density of low activation Mg 11 B 2 superconductors were systemically studied from low temperature to high temperature. It was found that the J c and H irr values of Mg 11 B 2 bulks in present work are both obviously higher than that of those samples prepared in previous studies. Furthermore, the low-temperature sintered samples exhibit better J c performance at high fields than the high-temperature sintered samples, due to strong grain boundaries pinning. On the other hand, the high-temperature sintered samples have higher J c at low fields compared to low-temperature sintered samples, mainly owing to their better crystallinity and grain connectivity. The highest J c value (2.20 ×10 5 A cm −2 at 20 K, self-field) is obtained in the Mg 11 B 2 sample sintered at 850 °C for 45 min. [ABSTRACT FROM AUTHOR]

Extending the holding time and slightly excessive Mg addition and Mg-Cu co-addition are introduced to the MgB 2 superconductors prepared by ex-situ sintering method aiming to improve their grain connectivity and J c. The influence of which on superconducting performance and microstructure of ex-situ sintered MgB 2 was also systemically studied. The A F value of Mg-added samples is obviously improved, especially the A F value of the Mg-Cu co-addition sample has reached the level of the in-situ sintering samples. The J c of two samples with Mg addition is improved by comparing to others within the entire whole field. [ABSTRACT FROM AUTHOR]