新型铁基超导线带材的研究进展

新型铁基超导材料具有较高的临界转变温度、超高的上临界场和非常小的各向异性等优点,在高场磁体领域应用前景广阔。目前粉末装管法已广泛应用于铁基超导线带材的制备,临界电流密度在4.2 K和10 T下高达1.7×104 A/cm2,接近实用化水平。首先介绍了铁基超导材料的典型结构与基本超导特性,详细评述了铁基超导粉末的合成和粉末装管法的工艺流程,主要包括元素配比、热处理工艺以及粉末装管原位法和先位法的对比分析,重点探讨了影响线带材临界电流密度的因素及其关键制备技术。通过包套材料的选择、掺杂改性、热等静压和轧制织构等方法来解决线带材中包套与超导芯易反应、杂相多、致密度低以及晶界弱连接等难题。此外还简要介绍了多芯线带材的最新研究进展。最后,对铁基超导线带材的发展趋势做了展望。     

MgB_2多芯超导线带材研究进展

回顾了近年来多芯MgB2超导线带材的主要研究进展,分析了包套材料的选取原则;比较了粉末套管法(PIT)、连续粉末装管成型工艺(CTFF)及中心镁扩散工艺(IMD)等几种常用的MgB2线带材加工制备技术的特点;评述了多芯MgB2线带材的磁通钉扎性能、交流损耗、稳定性与失超传播以及力学性能等方面的研究进展;同时简要回顾了多芯MgB2超导线带材的应用研究现状。     

“122”体系铁基超导线带材研究进展

简单介绍了“122”体系铁基超导材料的物理性能及优点,详细综述了“122”体系铁基超导线带材的研究进展,如制备方法、临界电流密度影响因素,并展望了“122”体系铁基超导线带材今后的研究方向.     

铁基超导材料的探索和研究进展

首先回顾了发现铁基超导体的历史,然后从材料学的角度,根据晶体结构的不同,系统地介绍和总结了目前发现的所有铁基超导材料.同时简要介绍了近期新铁基超导材料探索方面的进展以及单晶生长方面的工作.最后根据铁基超导体表现出来的奇特物理性质展望了铁基超导体的物理研究和应用前景.     

新型铁基超导线带材研制获进展

<正>在科技部、北京市科委、国家自然科学基金委的大力支持下,中科院电工研究所应用超导重点实验室马衍伟研究小组在新型铁基超导线带材的制备及其性能研究中取得重要进展。采用轧制织构和化学掺杂相结合的方法,研制出目前世界上临界传输电流性能最高的铁基线带材。该成果发表在由美国物理学会主办的《应用物理快报》(Appl.Phys.Lett.)上。这种方法的主要优点是工艺简单,成本低廉,有利于规模化制备。     

我国在二硼化镁线带材制备及其性能研究取得新进展

中科院电工所应用超导重点实验室和日本东北大学等合作,在新型超导材料二硼化镁（MgB2）线带材制备及其性能研究中取得系列新进展。通过对掺杂物以及掺杂机理的分析研究,采用多种有机物对MgB2线带材进行掺杂,大幅度提高了MgB2线带材在高磁场下的临界电流密度,研制出了多种具有国际先进水平的高性能MgB2线带材,如临界电流密度高达10800A／cm^2（4.2K,12T）。     

铁基超导体的磁性研究

介绍了超导电性的发展简史及其广阔用途,介绍了铁基超导体的结构分类和物质的磁性分类;以BaFe2As2为例综述了铁基超导体中铁磁和超导共存的研究现状,同时以SmOCoAs为例研究了1111相中丰富的磁结构,从而阐明磁性在铁基超导电性研究中的重要地位;最后针对高温超导微观机理研究和超导新材料探索提出了见解.     

铁基超导体与氧化铜超导体的超导机理不同

美国国家标准与工艺研究所（NIST）的中子研究中心利用中子束发现了铁基超导体的不同超导机理。这个单位的科学家首先发现了“掺杂”如何影响铁基超导体的磁学及超导特性。     

二硼化镁超导线带材及磁体应用研究进展

由于具有超导转变温度（39K）较高,晶体结构简单,原材料成本低廉以及长线制备容易等一系列特点,金属间化合物二硼化镁（ MgB2）超导体自2001年被日本科学家发现以来,引起人们广泛的关注,被认为是目前最有可能首先实现大规模工业应用的超导材料。尤其在制冷机工作温度（15～20 K）、较低磁场（1～2 T）条件下的医疗核磁共振成像仪（ MRI）超导磁体应用上有着广泛的前景。本文主要围绕实用化 MgB2超导长线（带）制备研究而展开,重点回顾了近年来粉末套管法、连续粉末装管成型法及中心镁扩散法等MgB2超导线（带）材制备及加工方面的最新研究进展;同时综述了在 MgB2超导线带材工程临界电流密度性能改进方面的最新研究工作;最后,对近几年来 MgB2超导磁体及线圈等应用研究进展进行了回顾。     

AC losses in multilayer superconducting tapes

ac losses have been investigated experimentally as well as theoretically in tapes having on the surface several normal conducting and/or superconducting layers. The superconducting layers under investigation have been Nb₃Sn on a niobium substrate and Nb₃Ge on a stainless steel substrate. It has been proved that the layered structure of the tapes is well reflected by the stepwise character of the ac losses dependence on the amplitude of the surface magnetic field. The magnetic flux passing through a surperconducting layer or surface barrier into the inside of the tape enhances the losses in the passed barrier or layer.     

Exploration of new superconductors and functional materials,and fabrication of superconducting tapes and wires of iron pnictides

Abstract

This review shows the highlights of a 4-year-long research project supported by the Japanese Government to explore new superconducting materials and relevant functional materials. The project found several tens of new superconductors by examining ～1000 materials, each of which was chosen by Japanese experts with a background in solid state chemistry. This review summarizes the major achievements of the project in newly found superconducting materials, and the fabrication wires and tapes of iron-based superconductors; it incorporates a list of ～700 unsuccessful materials examined for superconductivity in the project. In addition, described are new functional materials and functionalities discovered during the project.     

Experiments on flux jumps in superconducting tapes

Experimental results are reported on flux jumps measured by means of search coils on a short sample superconducting tape in an increasing field perpendicular to its surface. The superconducting material, the stabilizing copper thickness, the cooling condition, and the transport current have been varied during the tests. A small coil wound with a superconducting tape was also tested in a increasing perpendicular field. The flux jumps measured here are classified on the basis of their characteristics observed in the experiment.     

Development of Bi-oxide superconducting tapes and coils

We have developed Bi-2212 and 2223 tapes. For Bi-2212, two double stacked pancake type coils were fabricated using Bi-2212/Ag tapes prepared by a combination of the continuous dip-coating process and melt-solidification. A small coil (13 mm inner bore, 46.5 mm outer diameter) was inserted in a conventional superconducting magnet system. In a bias field of 20.9 T, the generated field of the coil was 0.9 T, at an I_c of 310 A (criterion 10⁻¹³ Ωm) at 1.8 K. Thus, the superconducting magnet system achieved the generation of a field of 21.8 T in the full superconducting state. A large coil (20 mm inner bore, 94 mm outer diameter) generated a field of 2.6 T (I_c = 385 A (10⁻¹³ Ωm)) at 4.2 K and 1.53 T (I_c = 225 A (10⁻¹³Ωm)) at 20 K in self-field. For Bi-2223, tapes were prepared by the powder-in-tube technique using Ag-10% Cu-x%M (x = 0–1.0, M = Ti, Zr, Hf or Au) alloy sheaths. The high J_c values of 5–7 × 10⁴ A cm⁻² at 4.2 K and 14 T were obtained for the tapes doped with x = 0.03–0.1 at.% Ti, 0.1 at.% Zr, 0.1 at.% Hf or 0.3% Au. These tapes have a modified Bi-2223 grain structure at the sheath/core interface and also a dense and more aligned microstructure, resulting in higher J_c values.     

Mechanical tests on the surface-coated Bi-2212 superconducting tapes

The strain dependence of the critical current of surface-coated Bi-2212 tapes is reported. Two methods are used in the measurements. The effect of bend strain on the critical current is obtained by a stepped cone apparatus. Peak stress or strain dependence of the critical current and the effect of the number of strain cycles on the critical current is also studied on multiple samples by employing a new in situ stress/strain device. The results show that the number of strain cycles does not significantly affect the critical current. Rather, the critical current of the tape depends only on the level of peak strain.     

Anisotropy of the critical current density in superconducting niobium-titanium wires

The critical current density in wires of an Nb-64 at % Ti alloy was determined in axial and circular directions by various methods. Owing to the cell structure due to cold deformation an anisotropy in the critical current density (j_{c, axially} <j_c, circularly) is present in the wires There is no major difference between magnetization currents and transport currents. Therefore it should be possible in principle to obtain the high critical current densities determined from circular magnetization currents by suitable defect structure with axial transport currents too.     

Measurement of the stability of overheated superconducting niobium-titanium wires

A method of measuring the stability of niobium-titanium wires when they are overheated is described. It is shown that the reliability of superconducting wires may be described by a combined integral parameter. This information is useful when the characteristics of the superconducting magnet's protection facility is chosen or the superconducting commutator's reliability is estimated. Experimental data are presented for commercial wires of differing diameter, sc: Cu ratio, matrix material and wire construction.     

Bi系2223高温超导带材力学性质

对4种Bi系2223高温超导带材77 K下的力学性质进行了实验研究.通过选择合适的合金包套替代传统的银包套,带材的机械性能能有所提高,但电学性质有所降低,尤其是内包套采用合金、外包套采用银,其机械性能反而低于纯银包套带材.通过X射线衍射图谱发现,当包套采用合金材料,尤其是内包套采用合金、外包套仍采用纯银,会大大降低样品中2223相的体积含量.相比较临界电流密度,n值对材料的破坏更为敏感.利用X光同步辐射技术初步探讨了银包套带材在室温和77 K下的损伤破坏过程.     

Deformation of silver-sheathed oxide superconducting tapes by trapped gases

A simple model was developed to describe the deformation in long silver-sheathed oxide superconducting tapes caused by the thermal expansion of air trapped within the conductor and by carbon dioxide released by the decomposition of SrCO₃ in the precursor powder during heat treatment. The analysis presented can be extended to include other carbon-containing compounds, impurities and gases released during the annealing process. The model assumes a zero-strain deformation process of the thin silver sheath in response to the gas pressure developed within the conductor due to heating. Results show that swelling (uniform deformation along the conductor length) increases linearly with temperature. For a carbon-free tape, swelling increases with decreasing precursor powder packing density. The reverse is true for tapes that contain carbon which is distributed uniformly within the tape. A carbon content of ≈0.001% by weight produces swelling similar to that produced by air. Increasing carbon content increases swelling. Carbon content in excess of 0.5% by weight will deform the conductor to the extent that elastic/plastic deformation can occur. Discrete SrCO₃ particles dispersed among the precursor powder produce bubbles (localized deformation). The size and concentration of these bubbles depend on the SrCO₃ particle size and concentration. For a given carbon content, small SrCO₃ particles form a large number of bubbles, which merge together resulting in swelling along the conductor length. Large SrCO₃ particles, on the other hand, form only a few discrete bubbles whose size increases with particle size.