TiB_2掺杂MgB_2超导线材临界电流密度和显微结构研究

Investigation on the Critical Current Density and Microstructure of TiB_2-doped MgB_2 Wire

以低碳钢管为包套材料,采用原位粉末套管法制备出5mol%TiB2掺杂的MgB2超导线材。利用X射线衍射、扫描电子显微镜、能谱分析和标准的直流四电极电阻法分别测试了线材的物相组成、显微结构、化学组成和临界电流密度(Jc)。结果显示,TiB2掺杂能够提高MgB2线材的Jc,使其达到了9960A/cm2(6K,4.5T)和1110A/cm2(6K,7T),比未掺杂线材分别提高了14%和26%。TiB2掺杂引起的MgB2晶粒减小,晶界面积增加和晶粒连结性改善,是Jc提高的主要原因。在未掺杂MgB2线材中还发现了微裂纹、MgO晶须等不利于超导性能的特殊显微结构。

5 mol% TiB_2 doped MgB_2 wire is fabricated through the in situ powder-in-tube method in flowing argon by using low carbon steel tube as sheath material. Phase compositions, microstructure features, chemical components and critical current density (J_c) of the doped and the undoped MgB_2 wires are investigated by using X-ray diffractometer, scanning electron microscopy, energy dispersive spectrometer and the standard four-probe resistance technique, respectively. It is found that J_c values are enhanced by TiB_2 doping. J_c of the doped wire reaches 9960A/cm 2 (6K, 4.5T and 1110A/cm 2 (6K, 7T), respectively, increasing about 14% and 26% compared with those of the pure MgB_2 wire. The decrease of MgB_2 grain size and the improved grain connection caused by TiB_2 doping are responsible for the enhancement of J_c. It is noted that some special microstructures, such as microcracks and nanometer MgO whiskers, are found in the pure MgB_2 wire, which are harmful to the enhancement of supeconducting properties.