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题名	掺杂MgB2带材和新型铁基超导线材的制备与性能研究; 掺杂MgB2带材和新型铁基超导线材的制备与性能研究
作者	1高召顺,电工研究所
学位类别	博士
答辩日期	2009-05-25
授予单位	中国科学院电工研究所
导师	1马衍伟,电工研究所
关键词	MgB2 铁基超导体 超导线带材 临界电流密度 掺杂 磁通钉扎 MgB2 iron-based superconductor superconducting wires and tapes critical current density doping flux pinning
其他题名	掺杂MgB2带材和新型铁基超导线材的制备与性能研究
中文摘要	2001年1月，日本科学家发现了迄今为止临界温度最高的金属间化合物超导体MgB2。与传统低温超导体相比，MgB2具有临界温度高（Tc＝39 K）、无弱连接、成本低廉、成材和加工性能较好等优点，在核磁共振成像（MRI）磁体领域具有广泛的应用前景。2008年2月，铁基超导体的发现为超导研究带来了新的契机，铁基超导体不仅在基础研究上有重要的意义，在应用方面也表现出乐观的前景。 论文第一部分主要研究了NbC和ZrC等过渡金属碳化物掺杂对MgB2带材超导性能的影响。研究表明，NbC掺杂可以改善晶粒连接性，使其在20 K、5 T下的临界电流密度Jc > 1.27  104 A/cm2，达到了国际先进水平。但是过渡金属碳化物反应活性非常差，即使在比较高的温度下，碳元素仍不能掺入MgB2晶格中，很难提高MgB2的上临界场Hc2。 论文第二部分通过系统的有机物掺杂实验，研究了掺杂量、热处理温度、晶粒连接性等对MgB2超导性能的影响。发现多种有机物掺杂能够显著提高MgB2带材在高场下的载流能力。其中马来酸酐掺杂样品的Jc高达1.08 104 A/cm2（4.2 K, 12 T），达到国际先进水平；硬脂酸掺杂样品的不可逆场Hirr在20 K时为10 T，超过了 NbTi 超导线在4.2 K下的水平。另外，还首次系统研究了不同氧含量的有机物掺杂对MgB2线带材临界电流密度的影响。结果表明，高的氧含量往往造成MgB2连接性的下降，最终导致其临界电流严重退化。 论文第三部分研究了空心碳球掺杂对MgB2带材的影响。实验发现空心碳球掺杂大幅度提高了MgB2带材的Hc2和Jc-H性能，在4.2 K和12 T条件下，样品的临界电流密度达到1.42 ×104 A/cm2，已经超过目前SiC掺杂MgB2的最好性能。研究表明，空心碳球中的碳元素可以有效地进入MgB2晶格，相应提高了MgB2超导材料的上临界场；另一方面，空心碳球掺杂对晶粒的细化作用显著提高了样品的磁通钉扎能力。 论文第四部分系统研究了掺杂对MgB2的上临界场、磁通钉扎特性和超导连接性的影响机理。由于MgB2具有两能带结构，相对于单能带超导体MgB2具有更多的电子散射渠道。可以通过调节电子散射的相对强度，获得比单能带超导体更高的上临界场。在MgB2材料中，晶界钉扎占主导作用，通过掺杂细化晶粒可以提高MgB2的磁通钉扎能力。孔洞和分布在MgB2晶粒间的杂相可能降低样品的有效传输面积，阻碍超导电流通过。研究表明MgB2的超导连接性还有很大的提升空间。通过对比各种掺杂物对MgB2临界电流密度的影响，总结并提出了掺杂物的选取原则。 论文第五部分主要介绍了一步法制备新型铁基超导线材和块材的工艺流程及性能表征结果。采用粉末装管（powder in tube）方法，研制出世界上第一根新型铁基超导体线材—La(O1-xFx)FeAs线材。在此基础上，通过优化工艺条件，制备出了Tc高达52 K 的Sm(O1-xFx)FeAs线材，其上临界场（T = 0）超过120 T，显示出该材料在高场磁体中的应用潜力。同时，在国际上首创了粉末装管法一步合成Sm(O1-xFx)FeAs超导块材的新工艺，并与传统的石英封管法制备的样品性能进行了比较。结果表明，一步法能减少样品的孔洞，提高F的掺杂效果，其Tc达到54.6 K，而且该方法更加简单、安全，同样也适用于其它新型铁基超导材料的制备。 The discovery of superconductivity at 39 K in the MgB2 has generated great interest in the field of applied superconductivity. It is considered as one of the most promising material for MRI magnet due to its high critical temperature (Tc), low material cost and weak-link free grain coupling. The recently discovered quaternary arsenide oxide superconductor La(O1-xFx)FeAs with the superconducting critical transition temperature of 26 K, has triggered great interest in both fundamental studies and practical applications. In the first part of this thesis, we have investigated the influence of transition metal carbide additions on the properties of MgB2 tapes. We found that the Jc values at 20 K were greatly improved by NbC addition, which can be attributed to the densification effect of NbC dopant. However, the carbon from transition metal carbide is not effective in entering the MgB2 structure, hence, hardly changing the Hc2 of MgB2. In the second part, we have synthesized organic compounds doped MgB2 tapes and succeeded in significantly improving the transport Jc in high magnetic fields. For example, at 4.2 K and in a field of 12 T, the Jc value of maleic anhydride (C4H2O3) doped sample reached 1.08 104 A/cm2, more than 25-fold improvement compared to the pure samples. In particular, the Hirr of stearic acid (C18H36O2) doped tapes achieved ~10 T at 20 K, exceeding that of NbTi at 4.2 K. The influence of variable oxygen contents of organic dopants on the superconducting properties of MgB2 tapes was also studied. The transport Jc and the connectivity were observed to decrease as oxygen contents of dopants increased. The more MgO and porosity formed during the reaction in C4H4O4 doped samples can be responsible for its low Jc values. As a result, the oxygen contents decrease in the starting material would be a key point to further enhance the transport Jc of MgB2. In the third part, we have synthesized the hollow carbon spheres (HCS) doped MgB2 tapes and investigated the influence of the HCS dopant on the superconducting properties of MgB2 tapes. At 4.2 K, the transport Jc for the HCS doped samples reached 3.1104, and 1.4104 A/cm2 at 10 and 12 T, respectively, even better than those of optimal nano-SiC doped tapes. C substitution-induced Hc2 enhancement as well as the strong flux pinning centers induced by grain boundaries are responsible for the superior Jc-H performance of the HCS doped samples. In the fourth part, the mechanism of transport Jc-H enhancement of MgB2 tapes with different dopants was discussed in detail. The multiple scattering channels provide the essential flexibility to increase the Hc2 of MgB2 to a much greater extent than in one-gap superconductors by optimizing the relative weight of the π and σ scattering rates. The dominant pinning centers of MgB2 are grain boundaries. The fine grain size caused by doping would create many grain boundaries that may act as effective pinning centres to improve the Jc-H property of MgB2 tapes. The connectivity is another important factor for further improve the transport Jc of MgB2. Based on the analysis, we suggested some principles for the selection of dopants. In the end of this thesis, we report the synthesis and the physical characterization of iron pnictide wires and bulks prepared by the powder-in-tube method (PIT). The LaO1-xFxFeAs wires were fabricated by this method for the first time. By optimizing the process, we have prepared Ta clad SmO1-xFxFeAs wires with the transition temperature of 52 K and a much high Hc2(0) above 120 T, indicating a very encouraging application of the new superconductors. We also applied the one-step PIT method to synthesize the iron-based bulks, due to its convenience and safety. Comparing with two-step method, one-step PIT method can reduce the porous area of samples and improve the doping effect of F element.
语种	中文
公开日期	2010-10-18
页码	118
分类号	TM1
内容类型	学位论文
源URL	[http://ir.iee.ac.cn/handle/311042/6788]
专题	电工研究所_其他部门_其他部门_博士学位论文
推荐引用方式 GB/T 7714	1高召顺,电工研究所. 掺杂MgB2带材和新型铁基超导线材的制备与性能研究, 掺杂MgB2带材和新型铁基超导线材的制备与性能研究[D]. 中国科学院电工研究所. 2009.

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