Superior critical current density obtained in Mg11B2 low activation superconductor by using reactive amorphous 11B and optimizing sintering temperature

The un-doped Mg 11 B 2 and Cu-doped Mg 11 B 2 bulks using 11 B as a boron precursor were fabricated by solid-state reaction and sintered at different temperature in present work. By analyzing the sintering process, it was found that 11 B original powder is more reactive and can react with Mg severely even at low temperature before Mg melting, which leads to the formation of refined Mg 11 B 2 grains. Consequently, the critical current density of Mg 11 B 2 sample prepared in this work is higher than that of natural MgB 2 . Furthermore, it was found that proper Cu addition could obviously accelerate the reaction between Mg and 11 B and promote the formation of Mg 11 B 2 due to the appearance of Mg–Cu liquid at low sintering temperature before Mg melting. On the other hand, Cu addition also introduced more MgCu 2 impurity, leading to a relatively lower critical current density on the whole. Interestingly, the critical current density of the Cu doped sample sintered at 800 °C is surprisingly enhanced at the low field, compared with that of the corresponding un-doped one. This is due to the peritectic reaction which generated small-sized MgCu 2 occurred that at 800 °C, providing MgCu 2 pinning centers well-distributed in the MgB 2 matrix.