原位法MgB_2-B_4C复相超导体合成及相含量调控研究

Research on the phase formation and fraction control of superconducting MgB_2-B_4C composite synthesized in situ

以B4C和Mg为原料合成的MgB2-B4C复相超导体具有高的临界电流密度(Jc)和高的超导转变温度(Tc),是一种有潜力的实用MgB2超导材料,其成相机理对复相MgB2超导体的相含量调控和磁通钉扎研究具有重要意义。结合经典烧结理论,研究了B4C-Mg真空固相烧结制备MgB2-B4C复相超导体的超导相形成和晶粒生长过程,给出了B4C-Mg的金斯特林格扩散模型和MgB2晶粒生长过程。通过选择B4C原料粒径,MgB2-B4C复相超导体超导相体积相含量在18%-88%范围可控。相含量88%的MgB2-B4C复相超导体临界转变温度达33.5K,转变宽度1.5K。10 K环境6T外场下电流密度可以达到1×104A/cm2,表明MgB2-B4C复相超导体具有良好的磁通钉扎行为。

The superconducting MgB2 -B4C composite, fabricated by just using two raw materials B4C and Mg, exhibits a high critical current density （ Jc ） and a high superconducting transition temperature （ Tr ） and has potential for high - power ap- plications. The MgB2 phase formation mechanism is significant to the volume fraction control of superconducting phase and flux pinning studying in MgB2 composites. Based on the classical sintering theory, MgB2 phase formation and grain growth in super- conducting MgB2 -B4C composites synthesized by vacuum solid state reaction, were investigated. We considered that B4C -Mg reaction process could be explained well by Ginstling diffusion mode]. The volume fraction of MgB2 phase in the superconducting MgB2 - B4C composites ranged from 18% to 88% by using different grain sizes of B4C raw material. A sample with 88% MgB2 fraction showed a critical transition temperature of 33.5 K, a transition width of 1.5 K, and a remarkable in -field current densi- ty of 1 × 104 A/cm2 under 6T at IOK. Those results indicate that superconducting MgBz - B4C composite has an excellent flux pinning behavior.