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1.
MgB2作为迄今为止超导转变温度最高的合金超导体,由于其具有结构简单、相干长度长、晶界间不存在弱连接、上临界场很高、电-声散射时间短等特点,MgB2超导薄膜在电子学领域有着广阔的的应用前景。拉曼光谱是研究电-声子相互作用和超导能带的一种有效方法,且已广泛用于分析MgB2材料的电子、声子特征以及超导体能带结构,研究表明,样品质量、晶粒尺寸以及测试条件对MgB2拉曼峰的峰位和峰形影响很大,其中拉曼光谱随温度的变化也是一个研究重点,但目前关于MgB2变温拉曼光谱的研究,测试的温度范围相对较小,局限在83 K到室温区域或是转变温度附近。研究了大范围温度区间内MgB2薄膜的拉曼光谱变化,采用混合物理化学沉积法在(0001)SiC衬底上制备了MgB2多晶薄膜,薄膜的晶粒尺寸约为300 nm,超导转变温度为39.3 K,对其在10~293 K之间的拉曼光谱进行了测试,测量的波数范围为20~1 200 cm-1。变温拉曼光谱的测试结果显示,在高频620 cm-1附近以及低频80和110 cm-1附近存在MgB2的拉曼峰。经分析,低频区域出现的两个拉曼峰的频率与超导能隙宽度相对应,表明MgB2的双能隙特性。考虑到MgB2中四种声子模式的拉曼活性,高频620 cm-1附近的拉曼峰应是由E2g振动模所贡献的,且随着测试温度的降低,该拉曼峰的峰位未发生明显的偏移,但半高宽显著变小,从293 K时的380.7 cm-1减小到10 K时的155 .7 cm-1,分析表明E2g声子与电子系统的非线性耦合所引起的非简谐效应可能是拉曼峰半高宽线性变小的主要原因。 相似文献
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K.M. Subhedar R.S. Hyam M.B. Kadam R.S. Kalubarme B.B. Sinha S.H. Pawar 《Physica C: Superconductivity and its Applications》2006,450(1-2):66-70
The comparative study of MgB2 film growth on Al2O3 and glass substrate by electrocrystallization technique is discussed. The precursor magnesium films were deposited by vacuum evaporation method. These magnesium films were then used as electrode for the growth of MgB2 films by electrocrystallization. The structural, morphological and superconducting properties of the electrocrystallized MgB2 films on Al2O3 substrate were examined by using XRD, SEM and electrical resistivity measurement techniques and compared with that of MgB2 films grown on glass substrate. The films deposited on Al2O3 substrates showed enhanced crystallinity and relatively higher Tc value compared to films deposited on glass substrates. 相似文献
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P.N. Togoulev N.M. Suleimanov K. Conder 《Physica C: Superconductivity and its Applications》2006,450(1-2):45-47
The temperature dependence of microwave absorption hysteresis is measured in superconducting composites, prepared from MgB2 and powders of magnetic Ni, Co, and non-magnetic Ti. In MgB2–Ni and MgB2–Ti composites the increase of microwave absorption hysteresis, by 150% and 25%, respectively, is found. In both cases this is connected with pinning enhancement. In MgB2–Co composites a decrease of the superconducting transition temperature and worsening of pinning properties are observed. 相似文献
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报道了两种新型超导体MgB2,MgCNi3和氧化物高温超导体Bi2< /sub>Sr2Ca0.9Ce0.1Cu2O8+y 的热导率-温度关系和电阻率-温度关系.实验发现氧化物高温超导 体在进入超导态后热导有所上升,出现极大值后再下降,而MgB2和MgCNi3 则单调下降. 由Wiedemann-Fra
关键词:
热导率
超导体
2')" href="#">MgB2
3')" href="#">MgCNi3 相似文献
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Soon-Gil Jung W.K. Seong W.N. Kang Eun-Mi Choi Heon-Jung Kim Sung-Ik Lee Hyeong-Jin Kim H.C. Kim 《Physica C: Superconductivity and its Applications》2006,450(1-2):114-117
The Hall resistivity (ρxy) and the longitudinal resistivity (ρxx) in c-axis-oriented superconducting MgB2 thin films have been investigated in extended fields up to 18 T. We have observed a scaling behavior between the Hall resistivity and the longitudinal resistivity, , where the exponent (β) is observed to be independent of the temperatures and the magnetic fields. For a wide magnetic field region from 1 to 18 T and a wide temperature region from 10 to 28 K, a universal power law with β = 2.0 ± 0.1 was observed in c-axis-oriented MgB2 thin films. These results can be well interpreted by using recent models. 相似文献
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以无磁性的Nb作为中心增强体和阻隔层材料,无氧铜作为稳定体包套材料,采用原位法粉末装管工艺(in-situ PIT)制备了千米量级7芯导体结构的MgB2/Nb/Cu超导线带材,由于Nb/Cu包套材料具有良好的塑形加工性能,整个加工过程中未进行中间退火热处理,复合多芯线材最终加工到Φ1.4mm;在真空热处理炉中680℃保温2小时进行成相热处理;对烧结后的线材进行了微观结构、超导电性、纵向电流分布均匀性及常温力学性能等分析检测.线带材的工程临界电流密度在20K,1T磁场条件下达到2.5×104 A/cm2.结果表明该工艺能够制备实用化高性能的MgB2线带材. 相似文献
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A. Tampieri G. Celotti S. Sprio R. Caciuffo D. Rinaldi 《Physica C: Superconductivity and its Applications》2004,400(3-4):97-104
The densification behaviour of MgB2 was studied when commercial powder was hot-pressed in the temperature range 1070–1190 °C. The mechanisms active during sintering were investigated by continuously recording the shrinkage vs. time and elaborating the data on the basis of Kingery’s model for liquid phase sintering. XRD and SEM analysis on final dense bodies were used to evaluate secondary phases formation during sintering and the effect of magnesium sublimation. AC magnetic susceptibility measurements were also performed to correlate the microstructural and morphological modifications induced by hot-pressing and the superconducting properties. 相似文献
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Single core stainless steel (SS) sheathed MgB2 tapes have been made by the powder-in-tube (PIT) method using commercial Mg and B powders in two series, one with nominal composition and the other with excess Mg. The electrical resistivity and susceptibility measurements have been carried out to evaluate residual resistivity ratio (RRR), the coherence length ξ(0) and critical current density JC(T) in these tapes. Detailed structural analysis of the core material has been carried out to correlate the superconducting properties with the crystallinity. In the optimized growth condition the MgB2 tapes exhibited an estimated JC of ∼1.4×107 A/m2 at 39.45 K in zero field and the zero temperature coherence length is found to be ∼68 Å. MgB2 tapes fabricated from starting powders having nominal Mg-composition have been shown to exhibit higher JC than those fabricated from excess magnesium composition of the starting powders. The strained lattice together with the presence of nanosized MgO inclusion having size smaller than the coherence length, are shown to be responsible for the observed higher JC. 相似文献
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A. Stenvall N. Magnusson Z. Jelinek G. Grasso I. Hiltunen A. Korpela J. Lehtonen R. Mikkonen M. Runde 《Physica C: Superconductivity and its Applications》2008,468(6):487-491
In this paper an electromagnetic system for a 200 kW MgB2 induction heater was designed to verify the feasibility of MgB2 superconductor in a DC induction heating system. The final master plan connects the electromagnetic design to the cryogenic and mechanical designs including the required measurement system. The electromagnetic design consists of conductor development, dimensioning the superconducting magnets and the quench protection system analysis. The coil system must guarantee appropriate heating distribution in the aluminium billet. The conductor has to fulfill the requirements of the current carrying capability required by the coil design. Furthermore, the conductor layout and constituent materials affect greatly to the coil stability in fault conditions. The coil behaviour during a fault was studied by quench simulations. The protection system design was based on the results of the quench analysis. 相似文献
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S.L. Budko R.H.T. Wilke M. Angst P.C. Canfield 《Physica C: Superconductivity and its Applications》2005,420(3-4):83-87
Measurements of the superconducting transition temperatures for Al-doped, C-doped and neutron-damaged–annealed MgB2 samples under pressure up to 8 kbar are presented. The dTc/dP values change systematically with the decrease of the ambient pressure Tc in a regular fashion. The evolution of the pressure derivatives can be understood assuming that the change in phonon spectrum is a dominant contribution to dTc/dP. 相似文献
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K. Rogacki K. Oganisian N. Zhigadlo J. Karpinski 《Journal of Physics and Chemistry of Solids》2008,69(12):3202-3204
The thermoelectric power of C, Mn, C:Li, and Al:Li substituted MgB2 single crystals has been investigated in the temperature range 10-300 K. Both the in-plane (Sab) and the out-of-plane (Sc) thermopowers are positive for the non-substituted crystal and both Sab and Sc change a sign for crystals doped with electrons where C is substituted for B in the amount larger than 5 at%. When Li is substituted for Mg, the π band rather than the σ band is doped with holes and the doping effects are much more subtle. The anisotropy ratio of the non-substituted crystal Sab/Sc≈3 and this ratio is strongly reduced by the substitution of C. Isovalent magnetic Mn ions, which substitute for Mg with a drastic reduction of Tc, do not influence the values and temperature dependences of both Sab and Sc. 相似文献
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Xiang-Rong Chen Hai-Yan Wang Yan Cheng Yan-Jun Hao 《Physica B: Condensed Matter》2005,370(1-4):281-286
We investigate the structure and the equation of state of compound MgB2 at high pressure using the full-potential linearized muffin-tin orbital scheme within the generalized gradient approximation correction in the frame of density functional theory. Through the quasi-harmonic Debye model, in which the phononic effects are considered, we have obtained successfully the bulk modulus and the thermal expansion of MgB2. 相似文献
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利用混合物理化学气相沉积法在石墨衬底上制备出了晶形为六角结构、厚度不同、径向尺寸不一的MgB2单晶纳米晶片. 利用纳米定向转移技术将此晶片转移到了碳支持膜铜网上, 以便对其精细结构等物性进行表征. 电输运测量和磁性测量结果都表明晶片具有超导电性: Tconset=38 K, Tc(0)=33 K. 扫描电子显微镜图像表明, 晶片表面平整、厚度分布在几个纳米到200 nm之间, 宽度从几微米到上百微米; 高分辨透射电镜图像显示出晶片具有周期性晶格条纹. 选区电子衍射数据与MgB2已有的单晶衍射数据相符. 这些测量结果证实了其确为高质量单晶MgB2超导纳米晶片. 本文不仅提出了一种全新的制备单晶MgB2的方法, 也观察到了纳米尺度MgB2单晶的零电阻现象, 为后续的磁通钉扎、纳米力学性能等领域的深入研究提供了合适的素材.
关键词:
2')" href="#">单晶MgB2
超导纳米晶片
零电阻
混合物理化学气相沉积法 相似文献
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在多晶系统的MgB2超导体中存在晶粒间较小的整体电流和晶粒内大的局域电流.用改变升温速率的方法制备了不同晶粒大小和晶粒连接性的MgB2样品,并对它们的晶粒大小进行了统计.采用一种测量超导临界电流密度的Campbell法,分别测量和计算得到了它们的整体电流和局域电流密度.研究表明:长时间的烧结造成晶粒变大,材料有较大的整体临界电流密度,而短时间烧结的样品则相反;同时发现晶粒细化只提高了样品的局域临界电流密度,而且样品内部缺陷、杂质及晶界等因素是影响MgB2超导体整体电流传输的主要因素. 相似文献
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MgB_2超导体输运特性的研究 总被引:3,自引:0,他引:3
文中对 Mg B2 超导体的制备过程 ,对其同位素效应、电阻率、I- V曲线、热电势、电导涨落效应、能隙、霍尔效应、热重 -差热分析实验等输运特性进行了较全面的综述 ,并讨论了在 Mg B2 超导体基础上的元素替代效应。 相似文献
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Kwang-Hua W. Chu 《Physica B: Condensed Matter》2011,406(1):80-83
We study the electric-field-driven transport of electrons in superconductors (CuxBi2Se3) by using the borrowed approach which has been successfully adopted to study the critical transport of other superconductors as well as supersolid helium in very low temperature environment. The critical temperatures related to the nearly frictionless transport of electrons were found to be directly relevant to the superconducting temperature of superconductors (CuxBi2Se3) after selecting specific activation energies. 相似文献