QQ客服 官方微博 反馈留言

题名	掺杂MgB2超导线带材的制备与性能研究; 掺杂MgB2超导线带材的制备与性能研究
作者	1张现平,电工研究所
学位类别	博士
答辩日期	2007-06-04
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 掺杂 磁通钉扎 临界电流密度 机理 MgB2, doping, flux pinning, critical current density, mechanism
其他题名	掺杂MgB2超导线带材的制备与性能研究
中文摘要	MgB2具有临界转变温度高、相干长度大、化学组成和晶格结构简单、原料价格低廉等优点，而且远比陶瓷性氧化物高温超导体容易加工成形。这些优越的特性使其在超导电力、电子器件、国防以及医疗仪器（特别是核磁共振成像磁体）等方面具有广泛的应用前景。本文系统研究了各种不同物理化学性质的物质掺杂对MgB2线带材微观结构和超导性能的影响。通过详细的分析和测试手段，探讨了纳米C掺杂提高线带材的临界电流密度的原因。分析了各种掺杂物质对MgB2线带微观结构和性能产生不同影响的机理。论文的主要内容如下： 1、采用ZrB2和ZrSi2对MgB2线带材进行了系统的掺杂研究。实验发现，和MgB2具有相同晶格结构的ZrB2进入MgB2晶体后产生类似于Mg位替代的晶格缺陷而起到钉扎中心的作用。在9 T（4.2 K），10％ ZrB2掺杂样品的临界电流密度达到6590 A/cm2以上。ZrSi2掺杂时，在热处理过程中和MgB2发生反应生成Mg2Si等杂质，部分纳米级杂质可以起到钉扎中心的作用。在10 T（4.2 K）条件下，5％ ZrSi2掺杂样品的临界电流密度相对于未掺杂样品提高10倍以上。 2、率先选用MoSi2、SiC晶须、Si/N/C等作为掺杂物质研究了硅化物掺杂对MgB2线带材微观结构和超导性能的影响。对于不能在MgB2相生成过程中分解的MoSi2来说，大部分粒子不但不能作为钉扎中心来提高材料的钉扎能力，而且会影响MgB2晶粒之间的连接性，因而掺杂后样品的临界电流密度提高不大。而对于能够发生分解的ZrSi2、SiC等物质来说，Mg2Si等杂质的生成提供了大量的钉扎中心，因而显著提高了材料的钉扎能力。更为重要的是，由于SiC掺杂时可以发生C对B的替代，不但会引入晶内钉扎中心，而且还影响到材料的能带散射，提高了MgB2材料的上临界场和不可逆场，因而样品的临界电流密度在10 T（4.2 K）时高达1.5×104A/cm2，达到世界先进水平。 3、首次系统研究了纳米C掺杂对MgB2线带材的影响。实验发现，随着C掺杂量增加或热处理温度的升高，MgB2的晶格常数a不断减小，表明C对B的替代量不断增加。MgB2衍射峰的半高宽随C掺杂量的增加而变大，说明C掺杂在MgB2超导芯中引入了杂质和晶格缺陷，这会提高样品的磁通钉扎能力。在10 T（4.2 K）时，8% C掺杂的MgB2带材样品的临界电流密度超过2.2×104A/cm2，这是目前世界上在C掺杂MgB2线带材中得到的最高数值。 4、采用标准四引线法直接测量了MgB2带材在各个磁场下电阻随温度的变化关系，得到了样品在5-35 K温度范围内上临界场和不可逆场数值。在4.2 K时，未掺杂样品的不可逆场仅为16 T，而950℃处理的C掺杂样品的不可逆场高达22.9 T，与Nb3Sn超导体的上临界场相当。在20 K时，C掺杂样品的不可逆场高达9 T，与Ni-Ti超导体在4.2 K下的上临界场相当。这些上临界场或不可逆场数值达到了目前国际先进水平。 5、分析了含碳类物质掺杂提高MgB2上临界场和不可逆场的原因。由于C比B多一个电子，C的替代会在σ带中引入电子，增加载流子的散射，减小它们的自由程，降低超导相干长度，进而提高MgB2材料的上临界场Hc2。与此同时，C对B替代导致的晶格畸变以及掺杂物质和MgB2反应生成的纳米级沉积物对于提高MgB2材料的磁通钉扎能力作用也十分显著。 As a promising candidate for engineering applications in the temperature range 20-30 K, MgB2 was hotly investigated since superconductivity in this compound was discovered. MgB2 has attractive characteristics as regards practical use, such as high critical temperature (Tc), ‘weak-link free’ grain coupling and low material cost. In this paper, the doping effect on microstructure and superconducting properties of MgB2 by different materials were systematically studied. The mechanism of the Jc-B property enhancement of MgB2 tapes doped with different materials was investigated. The main results are listed as follows: 1. The doping effects of ZrB2 and ZrSi2 on MgB2 tapes/wires were systematically studied. It is found that when small ZrB2 particles were incorporated into MgB2 lattice, they can act as pinning centers to enhance the flux pinning ability of MgB2. In 10% ZrB2 doped MgB2 tapes, a Jc value higher than 6590 A/cm2 at 9 T (4.2 K) was reached. As ZrSi2 can be decomposed during the sintering process, many small impurity particles such as MgSi2 were incorporated into MgB2 matrix, and the flux pinning ability was improved. Compared to the undoped samples, a Jc value more than 10-fold improvement was found in 5% ZrSi2 doped samples at 10T (4.2 K). 2. Doping effect of silicates on phase composition, microstructure and superconducting properties were investigated. As MoSi2 could not discompose during the formation process of MgB2, most of the doped MoSi2 particles would damage the grain linkages of MgB2. But for ZrSi2 and SiC doping, some impurities such as Mg2Si, which were formed during the sintering process, could act as pinning centers to improve the flux pinning ability. Most importantly, there are substitutions of B by C happened in SiC doped samples, and the Hirr and Hc2 were improved. Jc values for the SiC doped samples were enhanced by two orders of magnitude at 4.2 K in magnetic fields above 8 T. At 4.2 K, 10 T, the Jc reached 1.5×104A/cm2. 3. The effect of nano-C doping on MgB2 tapes and wires was studied. The relationships between the critical current density, crystallinity and microstructure were systematically studied as functions of the C doping level and heating conditions. It is found that the a-axis length was decreased due to carbon substitution. The FWHM of the MgB2 (101) peak increases with increasing C doping level, suggesting the introduction of lattice defects and/or decrease of the crystal size of MgB2 occurred by C doping. At 4.2 K, 10 T, a Jc value higher than 2.2×104A/cm2 was obtained in 8% C doped samples sintered at 900 oC. 4. The resistance versus temperature measurements on the pure and C doped MgB2 tapes in various magnetic fields was performed by the four-probe resistive method. It is interesting to note that at 4.2 K, Hirr for the C-doped tape heated at 950 oC reached 22.9 T, compared to 16 T for the undoped one. This Hirr value was comparable to the Hc2 of a conventional bronzed-processed Nb3Sn conductor. Most importantly, at 20 K, Hirr reached 9 T for C-doped tapes heated at 950 oC, which was comparable to the Hc2 at 4.2 K of commercial Nb-Ti conductors. 5. The reason for the improvement of Hc2 and Hirr of MgB2 by C substitution was discussed. Because C has one more electron than B, it would add electrons in σ band when it came into MgB2 lattice, and the C in MgB2 lattice can act as electron scattering centers too. By the substitution, it can increases scattering of the charge carriers, reduces their mean free path, results in a decrease of the superconducting coherence length, and eventually leads to an increase of Hc2. This is one of the reasons why SiC and C doped samples have high Jc values in high magnetic fields.
语种	中文
公开日期	2010-10-18
页码	116
分类号	TM1
内容类型	学位论文
源URL	[http://ir.iee.ac.cn/handle/311042/6752]
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张现平,电工研究所. 掺杂MgB2超导线带材的制备与性能研究, 掺杂MgB2超导线带材的制备与性能研究[D]. 中国科学院电工研究所. 2007.

个性服务

查看访问统计

相关权益政策

暂无数据

收藏/分享

除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。