共查询到16条相似文献,搜索用时 125 毫秒
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以纳米Al粉为掺杂物质,借助超声分散,较好地解决了纳米Al粉的团聚及其与B粉的均匀混合问题,制备出了1mol%、2mol%、5mol%、8mol%纳米Al粉掺杂的MgB2超导块材,并对掺杂效果和机理进行了研究.物相和显微结构分析表明,Al能够替代Mg进入MgB2晶格内,并导致MgB2的晶胞参数a、c逐渐降低,其中c的降低幅度较大.随着Al掺量的增加,MgB2的临界温度疋逐渐降低,由未掺杂时的38.5K降低至掺杂8mol%Al时的35.5K.超导电性研究结果表明,纳米Al粉掺杂,在低温、高场、低掺杂量的条件下可以改善MgB2的超导性能,掺杂量过大反而抑制MgB2的超导性能,2mol%的纳米Al粉掺杂效果最好. 相似文献
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原料硼粉价格是决定MgB2超导材料制备成本高低的主要因素.不同纯度硼粉的价格相差十分悬殊.从降低原料成本的角度出发,MgB2超导材料的制备首选价格低廉的低纯度硼粉.然而,采用低纯度的硼粉所制备的MgB2的超导电性明显降低.为了提高用低纯硼粉制备的MgB2的超导电性,澳大利亚伍伦贡大学超导电子材料研究所进行了低纯原料硼粉的纯化处理,并研究了纯化处理后的硼粉对MgB2超导电性影响. 相似文献
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MgB2超导电性研究进展 总被引:4,自引:0,他引:4
2001年1月所发现的MgB2超导体具有39K的临界转变温度,是迄今为止转变温度最高的非铜氧化物超导体.它可能做为一种新型低成本高性能超导材料而受到广泛关注.本文简述了近期对MgB2超导体的研究工作,介绍了近期主要有关MgB2超导体电子结构研究和应用开发的工作,着重叙述了关于MgB2超导机制的研究. 相似文献
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SiC掺杂对MgB2/Fe超导线材临界电流密度和显微结构的影响 总被引:1,自引:0,他引:1
利用原位粉末套管法制备出SiC微粉掺杂的MgB2-x(SiC)x2/Fe(z=0.00、0.05、0.10、0.20)超导线材。在750℃,流通高纯氩气的条件下热处理1h后,大部分SiC没有参与取代B位的反应。随着x的增大,线材中非超导相SiC和Mg的含量增加,MgB2的平均晶粒尺寸变小,从而使可作为磁通钉扎中心的晶界的面积相应增加。在外加磁场中,MgB2超导线材的临界电流密度(Jc)随x增大逐步升高,至x=0.10时Jc性能最好,其在6K,5T时的Jc达到了8480A/cm^2,比未掺杂线材的Jc高出约70%。但是,当x=0.20时,Jc却有所下降。Jc的这种变化规律与SiC掺杂引起的MgB2晶粒变小,以及非超导相物质含量之间的相互平衡有关,其中MgB2晶粒变小是Jc提高的主要原因。 相似文献
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Shekhar C Giri R Malik SK Srivastav ON 《Journal of nanoscience and nanotechnology》2007,7(6):1804-1809
In the present study, we report a systematic study of doping/admixing of carbon nanotubes (CNTs) in different concentrations in MgB2. The composite material corresponding to MgB2-x at.% CNTs (35 at.% > or = x > or = 0 at.%) have been prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/microstructural characterization employing XRD, Scanning electron microscopic (SEM), and Transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by Physical property measurement system (PPMS) and electrical transport measurements have been done by the four-probe technique. The microstructural investigations reveal the formation of MgB2-carbon nanotube composites. A CNT connecting the MgB2 grains may enhance critical current density due to its size (approximately 5-20 nm diameter) compatible with coherence length of MgB2 (approximately 5-6 nm) and ballistic transport current carrying capability along the tube axis. The transport critical current density (Jct) of MgB2 samples with varying CNTs concentration have been found to vary significantly e.g., Jct of the MgB2 sample with 10 at.% CNT addition is approximately 2.3 x 10(3) A/cm2 and its value for MgB2 sample without CNT addition is approximately 7.2 x 102 A/cm2 at 20 K. In order to study the flux pinning effect of CNTs doping/ admixing in MgB2, the evaluation of intragrain critical current density (JJ) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on Jc is obtained for 10 at.% CNTs admixed MgB2 sample at 5 K, the Jc reaches approximately 5.2 x 10(6) A/cm2 in self field, -1.6 x 10(6) A/cm2 at 1 T, approximately 2.9 x 10(5) A/cm2 at 2.6 T, and approximately 3.9 x 10(4) A/cm2 at 4 T. The high value of intragrain Jc in 10 at.% CNTs admixed MgB2 superconductor has been attributed to the incorporation of CNTs into the crystal matrix of MgB2, which are capable of providing effective flux pinning centres. A feasible correlation between microstructural features and superconducting properties has been put forward. 相似文献
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Jiao Zhu Yi Bing Zhang Xiao Long Niu Chuang Chuang Lu Hong Mei Zhu Chuan Bing Cai 《Journal of Superconductivity and Novel Magnetism》2014,27(10):2205-2209
Superconducting magnesium diboride-magnesium oxide (MgB 2-MgO) composite attracts our attention due to its relatively high superconducting transition temperature close to the one of a pure MgB 2 bulk and metallic transport behavior with low resistivity in the normal state even at a high fraction of insulating MgO. In this paper, we report that the current-carrying capacities of MgB 2-MgO composites were enhanced by improving the replacement reaction process, and the superconducting MgB 2 fraction can be in situ controlled by using magnesium (Mg), boron trioxide (B 2 O 3), and boron (B) as the raw materials. The composites with mass fractions of superconducting MgB 2 from 27 to 80 % show that the zero-resistance transition temperatures are above 36.7 K, and the self-field critical current densities are from 0.2 ×106 to 4 ×106 A/cm 2 at 10 K. The high J cS of the superconducting composites under the applied fields prove that there is no appreciable difference between a perfect MgB 2 sample and one with MgO doping, but the critical current density and flux pinning are improved. These results are meaningful for studying further the flux-pinning mechanism in MgB 2. 相似文献
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Graphene is a wonder material with the ultimate smallest thickness that is readily accessible to various approaches for engineering its excellent properties. Graphene doping is an efficient way to tailor its electric properties and expand its applications. This topic covers wide research fields and has been developing rapidly. This article presents a broad and comprehensive overview of the developments in the preparation and applications of doped graphene including doping methods, doping levels, doping effect and types of heteroatoms. Very recent advances are also presented. In addition, existing problems in terms of achieving greater control over and further developments of doped graphene are also discussed. 相似文献
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MgB2高温超导体的发现,掀起了面向应用的MgB2成材研究的热溯。综述了MgB2线带材和薄膜的成材研究进展及应用前景。 相似文献
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Zeng X Pogrebnyakov AV Kotcharov A Jones JE Xi XX Lysczek EM Redwing JM Xu S Li Q Lettieri J Schlom DG Tian W Pan X Liu ZK 《Nature materials》2002,1(1):35-38
The newly discovered 39-K superconductor MgB2 holds great promise for superconducting electronics. Like the conventional superconductor Nb, MgB2 is a phonon-mediated superconductor, with a relatively long coherence length. These properties make the prospect of fabricating reproducible uniform Josephson junctions, the fundamental element of superconducting circuits, much more favourable for MgB2 than for high-temperature superconductors. The higher transition temperature and larger energy gap of MgB2 promise higher operating temperatures and potentially higher speeds than Nb-based integrated circuits. However, success in MgB2 Josephson junctions has been limited because of the lack of an adequate thin-film technology. Because a superconducting integrated circuit uses a multilayer of superconducting, insulating and resistive films, an in situ process in which MgB2 is formed directly on the substrate is desirable. Here we show that this can be achieved by hybrid physical-chemical vapour deposition. The epitaxially grown MgB2 films show a high transition temperature and low resistivity, comparable to the best bulk samples, and their surfaces are smooth. This advance removes a major barrier for superconducting electronics using MgB2. 相似文献
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系统综述了MgB2超导纳米结构的制备方法,包括基于广义模板法的两步法或多步法、反应烧结法、基于电子束刻蚀技术、高温直接分解法、溶胶-凝胶法和混合物理化学气相沉积法等。总结了MgB2超导纳米结构的生长机理,并且评价了这些方法的优缺点。 相似文献