SiC掺杂对MgB_2/Fe超导线材临界电流密度和显微结构的影响

Effect of SiC doping on the critical current density and microstructure of MgB_2/Fe wires

利用原位粉末套管法制备出SiC微粉掺杂的MgB2-x(SiC)x/2/Fe(x=0.00、0.05、0.10、0.20)超导线材。在750℃,流通高纯氩气的条件下热处理1h后,大部分SiC没有参与取代B位的反应。随着x的增大,线材中非超导相SiC和Mg的含量增加,MgB2的平均晶粒尺寸变小,从而使可作为磁通钉扎中心的晶界的面积相应增加。在外加磁场中,MgB2超导线材的临界电流密度(Jc)随x增大逐步升高,至x=0.10时Jc性能最好,其在6K,5T时的Jc达到了8480A/cm2,比未掺杂线材的Jc高出约70%。但是,当x=0.20时,Jc却有所下降。Jc的这种变化规律与SiC掺杂引起的MgB2晶粒变小,以及非超导相物质含量之间的相互平衡有关,其中MgB2晶粒变小是Jc提高的主要原因。

Micrometer size SiC powder doped MgB2-x(SiC)x/2/Fe (x=0.00, 0.05, 0.10, 0.20) wires were fabricated by using in situ powder-in-tube method. These wires were heat treated at 750°C for 1 h in flowing high purity argon. It was found that non-superconducting phase, SiC and Mg, exists in the doped wires and their contents increase with x. This means that most of the SiC particles did not participate the reaction that aimed at substituting B by Si and C atoms in MgB2 grains. It was revealed that the average MgB2 grain size decreases with the increasing of x, thus increases the area of grain boundary that can act as flux pinning centers effectively. Therefore, the critical current density (Jc) of MgB2 wires increases with x. The best Jc values was achieved in the wire x=0.10. For example, its Jc reaches 8480 A/cm2 at 6 K and 5 T, which was nearly 70 percent higher than the undoped wire. However, Jc of the wire dropped when x reached to 0.20. It was believed that the balance between the reduction of the MgB2 grain size and the increasing of the content of SiC and Mg was responsible for the variation trend of Jc, and the drop of MgB2 grain size was the main cause for the improvement of Jc.