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Abstract: The minor Cu (<3at%) addition could significantly reduce the amount of MgO impurity in the in situ sintered MgB2 samples and thus improve the critical current density (J c) at low field and the critical transition temperature (T c). The formation of local Mg–Cu liquid at about 485°C could wrap the neighboring Mg particles and thus protect them from the oxidation during the sintering process. Our results provide a possible route to further improve the superconductive properties of pure or doped MgB2 samples through decreasing the amount of MgO impurity with minor Cu addition. [Copyright &y& Elsevier]

Abstract: Based on the thermal analysis, microstructure observation and superconductivity measurement, the phase formation and superconductive properties of Cu doped MgB2 samples sintered with milled B powder were investigated. The minor Cu addition could prompt the solid–solid reaction between Mg and milled B and the formation of MgB2 phase is almost completed before Mg melting. The MgB2 grains near the local Mg–Cu liquid could grow faster than others during the phase formation of MgB2 before Mg melting. Furthermore, abnormal growth of these preferentially formed MgB2 grains could occur after Mg melting. Hence, the MgB2 grains in the Cu-doped samples are larger and less homogeneous than that in the undoped sample sintered with milled B powder. As a result, the pinning of grain boundaries is reduced obviously and the J c becomes more sensitive to the applied magnetic fields in the Cu-doped sample sintered with milled B powder. On the other hand, the accelerated solid–solid reaction between Mg and B would accompany with less residual Mg and thus the volatility of Mg is weaker after melting, which result in a higher density and fewer voids in the Cu-doped samples and thus enhance the grain connectivity between MgB2, finally lead to the improvement of J c at low fields. [Copyright &y& Elsevier]