共查询到19条相似文献,搜索用时 93 毫秒
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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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以Mg粉和B粉为主要原料,采用两种烧结方法制备出MgB2超导体.利用x射线衍射仪、扫描电子显微镜、阿基米德法和标准的直流四引线法等,分别研究了样品的物相组成、显微结构、密度和临界电流密度等.研究发现,MgB2块材的密度随Mg粉粒度的增加而降低.与常规烧结相比,快速烧结时MgB2块材的密度较低且含有更多的非超导相,如Mg和MgBx(x=4,6或12).快速烧结MgB2线材的临界电流密度低于常规烧结线材的.结果表明,快速烧结不利于获得高性能的MgB2超导体. 相似文献
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超导体MgB2的高温电阻率及热重—差热分析 总被引:1,自引:0,他引:1
利用Mg扩散法制备出单相多晶的MgB2超导体,其超导转变的零电阻温度为38.4K左右,转变宽度小于1K。正常态电阻率温度关系为金属型,在270K-450K的高温范围内电阻率与温度成很好的线性关系。差热和热重分析表明在空气气氛中MgB2在900℃左右开始急剧氧化。 相似文献
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用透射电子显微镜研究了Ti3SiC2材料中Ti3SiC2与TiC的界面关系。结果表明TiC和Ti3SiC2颗粒都可能生长在另一相中,Ti3SiC2中的TiC颗粒与Ti3SiC2没有明显的晶体学关系,而TiC中的Ti3SiC2与TiC之间有下列晶体学关系,(111)TiC//(0001)Ti3SiC2,(002)TiC//(1 1^-04)Ti3SiC2,(1 1^-0)TiC//「110」Ti2SiC2。 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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The experimentally observed ferromagnetism in MgB2 in the normal state is attributed to microphase-separated inclusions of iron. This magnetic character is also observed when the iron content of the samples is reduced below 20 g/g, however in these samples the diamagnetism of MgB2 is apparent and is measured. It is found experimentally that the diamagnetic susceptibility at room temperature of B element, MgB2, and MgB4 is close to the ratio 1:2:4, suggesting that the diamagnetism in these borides is confined to the boron atoms. This observation supports a picture in which the two electrons of Mg are donated to B in MgB2. 相似文献
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A. Agliolo Gallitto G. Bonsignore G. Giunchi M. Li Vigni 《Journal of Superconductivity and Novel Magnetism》2007,20(1):13-20
We report experimental results of second-harmonic (SH) response at microwave frequency in several ceramic MgB2 samples, prepared by different methods. The SH signal has been investigated as a function of the temperature and DC magnetic
field. The investigation has been carried out at low magnetic fields, where nonlinear processes arising from motion of Abrikosov
fluxons are ineffective. We show that the low-temperature SH emission is ascribable to processes involving weak links. Comparison
among the peculiarities of the SH signal radiated by the different samples shows that the presence of weak links strongly
depends on the sample preparation method, as well as on the purity and morphology of the components used for the preparation. 相似文献
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R. S. Gonnelli A. Calzolari D. Daghero D. Delaude M. Tortello G. A. Ummarino V. A. Stepanov N. D. Zhigadlo J. Karpinski P. Manfrinetti 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):555-558
We present the results of point-contact spectroscopy (PCS) measurements in single-phase Mg1−x
Al
x
B2 crystals and polycrystals with x up to 0.32, recently grown at ETH (Zurich) and University of Genova, respectively. The differential conductance curves of
our “soft” point contacts were measured as a function of temperature from 4.2 K up to the Andreev critical temperature T
c
A
, at which the normal-state conductance is recovered. The gap amplitudes, Δ
σ
and Δ
π
, were obtained through a two-band BTK fit of the normalized conductance curves. The results extend previous data to the range
of heavy Al doping and show that contrary to expectations, no gap merging is observed up to x=0.32 (i.e., down to T
c
A
=9 K). The analysis of the gap trends within the two-band Eliashberg theory shows that band filling is the main effect of
Al doping, even though a small increase in interband scattering might be necessary to account for the experimental data in
single crystals. 相似文献
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SiC and TiC coatings were deposited by CVD on graphite substrates and the effect of the variation of the methane (CH4) and hydrogen (H2) ratio on deposition was investigated. SiCl4, TiCl4 and CH4 were used as sources of Si, Ti and C. In case of the SiC coatings, stoichiometric SiC was obtained when the ratios of CH4/(SiCl4 + CH4)andH2/(SiCl4 + CH4) are 0.4 and 10, respectively. Stoichiometric TiC was also obtained under similar conditions. In order to obtain non-stoichiometric materials for possible fabrication of functionally gradient materials (FGM), a change of microstructure and composition was observed with changes of the CH4 and H2 ratio. As a result, SiC, TiC and C contents were more easily controlled by a change of the H2 ratio compared to the CH4 ratio for SiC and TiC deposition. It has been verified that the change of the H2 ratio is more desirable for possible manufacturing of SiC/TiC/C FGM. 相似文献
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Tinatin Kuchukhidze Archill Mikeladze Ekaterine Sanaia Guram Bokuchava George Darsavelidze Roin Chedia 《材料科学与工程:中英文B版...》2013,(12):793-798
Powder of magnesium diboride was obtained by solid phase reaction of mixture of magnesium (〉 99% pure) and amorphous boron (〉 99% pure) powders at 650-900 ℃ temperatures in inert atmosphere. During synthesis process main attention was paid. to removing oxide layer of surfaces of powder particles by organic solvents in Glovebox, where concentration of oxygen and water steam is less than 5 ppm. Homogenization and activation of powders were conducted in a planetary nano-mill by WC balls in an inert area. Pressing of the obtained powders was conducted in an argon atmosphere. MgB2 nonstoichiometric powders contained excess boron and magnesium, Magnesium hydride was used as source of excess boron, which is fragile compound and easy to grind in nano-mill. It decomposites with metallic magnesium and hydrogen up to 280 ℃ temperature. Commercial magnesium diboride powder (Aldrich, 〉 99%) was used for fabrication of MgB2 bulk targets. Powders systems of MgB2-Mg, MgB2-MgH2, MgB2-B homogenized by nano-mill in Glove box was used for fabrication of composites with nonstoichiometric contents. The targets were cylinders with diameters of 27-52 mm and height of 5-15 mm. Consolidation of pressed powdery composites was conducted in argon atmosphere. Synthesis of MgB2 from mixture of magnesium and amorphous boron powders and simultaneous consolidation were conducted by hot pressing (HP) method. Phase content of the obtained targets were established by XRD method after dry polishing. Superconducting characteristic of the obtained samples were measured by vibrational magnetometer. The superconducting transition with an onset at 39 K was observed in a good agreement with the results of the other groups obtained on samples prepared by conventional techniques. The phase exists near the nominal composition without a significant homogeneity range. 相似文献
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S. Sprio D. Rinaldi G. Celotti E. Pialorsi A. Tampieri 《Journal of Materials Science: Materials in Electronics》2008,19(10):1012-1022
The preparation of dense MgB2 bodies, undoped and doped with different atomic species (Na, Ag, Y), was performed via reactive sintering by uniaxial and
isostatic hot pressing, starting from the pure elements, and compared with undoped samples obtained by commercial MgB2 powder. The superconducting characteristics of the obtained materials, namely critical temperature (Tc) and current (Jc), were obtained through ac susceptibility measurements and compared to their structural features, like phase purity and secondary
phases formation and distribution in the MgB2 matrix. Both the adopted hot pressing techniques gave rise to undoped MgB2 pieces exhibiting phase purity in the range 85–95% and relative density above 80%; although in most cases the doped samples
underwent higher extents of phase decomposition and lesser densification, they all exhibited higher critical temperature and
current compared to the corresponding undoped material, indicating a net influence of the doping on the superconducting behaviour
of MgB2, particularly Ag and Y. An opportune quality factor was adopted, to obtain a more reliable comparison between the different
MgB2 samples and evaluation of the samples goodness, in relation to their superconducting characteristics. It was put in evidence
that low amounts of doping can improve the superconducting behaviour of MgB2 and that this influence can be addressed in terms of pinning centres, as there was no experimental evidence of an actual
atomic substitutions in the MgB2 crystal. 相似文献
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M.S.A. Hossain A. Motaman Ö. Çiçek H. Ağıl E. Ertekin A. Gencer X.L. Wang S.X. Dou 《低温学》2012,52(12):755-759
The effects of sintering temperature on the lattice parameters, full width at half maximum (FWHM), strain, critical temperature (Tc), critical current density (Jc), irreversibility field (Hirr), upper critical field (Hc2), and resistivity (ρ) of 10 wt.% silicone oil doped MgB2 bulk and wire samples are investigated in state of the art by this article. The a-lattice parameter of the silicone oil doped samples which were sintered at different temperatures was drastically reduced from 3.0864 Å to 3.0745 Å, compared to the un-doped samples, which indicates the substitution of the carbon (C) into the boron sites. It was found that sintered samples at the low temperature of 600 °C shows more lattice distortion by more C-substitution and higher strain, lower Tc, higher impurity scattering, and enhancement of both magnetic Jc and Hc2, compared to those sintered samples at high temperatures. The flux pinning mechanism has been analyzed based on the extended normalized pinning force density fp = Fp/Fp,max scaled with b = B/Bmax. Results show that surface pinning is the dominant pinning mechanism for the doped sample sintered at the low temperature of 600 °C, while point pinning is dominant for the un-doped sample. The powder in tube (PIT) MgB2 wire was also fabricated by using of this liquid doping and found that both transport Jc and n-factor increased which proves this cheap and abundant silicone oil doping can be a good candidate for industrial application. 相似文献