The accelerated formation of MgB2 bulks with high critical current density by low-temperature Cu-doping sintering

MgB2 bulks were successfully prepared by Cu-doping sintering at 575 degrees C for only 5 h, exhibiting an obvious decrease in the sintering time at low temperature. According to the thermal analysis, the local Mg-Cu liquid formed first during the sintering process and then provided higher transport than the solid for the diffusion of Mg atoms into B, resulting in an accelerated reaction between Mg and B. The measured critical current density (J(c)) of all the doped (Mg1.1B2)(1-x)Cu-x (x < 0.10) samples was 1 x 10(6) A cm(-2) in zero field at 20 K and about 1 x 105 A cm(-2) in 2 T field at 20 K, respectively. The excellent J(c) is mainly attributed to the grain-boundary pinning mechanism resulting from the formation of small MgB2 grains during the low-temperature sintering. Further, we found that with increasing the amount of Cu addition in the low-temperature sintered MgB2 samples, the predominant flux pinning mechanism of the doped sample varies from grain-boundary pinning to MgCu2-nanoinclusion pinning introduced by the reaction between Mg2Cu and residual B. This transition results in an abnormal increase of J(c) in the sintered (Mg1.1B2)(0.90)Cu-0.10 sample compared to the sintered (Mg1.1B2)(0.95)Cu-0.05 sample in which only Mg2Cu was found around the edge of voids.