共查询到20条相似文献,搜索用时 156 毫秒
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固相法合成系列名义组成为Bi2-xNbxSr2Ca2Cu3Oy(x=0—1.0)的样品,电学和磁学测量表明,当掺入x=0.2—0.3的Nb有明显加强2223相生成的作用,配比为Bi1.7Nb0.3Sr2Ca2Cu3Oy时最佳;当掺Ba以部分取代Sr后有明显协同Nb促进2223相生成的作用,比单掺Nb效果更为显著,其中以Bi1.7Nb0.3Sr1.8Ba0.2Ca2Cu3Oy为最优组成。热重分析(TGA)实验显示,掺Nb(Ba)后样品在~600°C出现吸氧增重;XPS中的O1s峰显示掺Nb(Ba)后除~531eV的主峰外,在~529eV的肩峰更加明显;讨论了Nb(Ba)对晶体结构的可能影响。
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用固相反应法合成了名义组分为Bi1.92Pb0.32Sr2Ca1.7Mg0.3Cu3.07Ox的块状样品。X射线衍射谱(XRD)、扫描电子显微镜(SEM)和电子探计X射线分析(EDAX)结果以及块状和粉状试样的交流磁化率测量表明,样品中存在110和85K两个超导相;2223相(110K)首先在2212相(85K)晶体的晶界和外部区域生成。本文认为,最初存
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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
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热导率
超导体
2')" href="#">MgB2
3')" href="#">MgCNi3 相似文献
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D. Ahmad I. Park G.C. Kim J.H. Lee Z.-A. Ren Y.C. Kim 《Physica C: Superconductivity and its Applications》2009,469(15-20):1052-1054
The irreversibility line and flux pinning properties of high-Tc superconductor SmFeAsO0.85 were studied using DC magnetization data. Polycrystalline SmFeAsO0.85 was prepared in a high pressure synthesis apparatus under the pressure of 6 GPa. The results of DC susceptibility showed the superconducting transition at about 55 K. A critical current density Jc(B) was calculated using Bean’s critical state model. At low temperatures (20 K), Jc(B) showed a relatively high value with weak dependence on an applied magnetic field. At higher temperatures, a stronger dependence of the magnetic field was observed, which resulted from decrease in a critical current density probably due to the flux creep effect. The irreversibility line (IL) agreed well with the flux creep theory of Matsushita et al. A comparison of normalized pinning force density with the theoretical models showed that the irreversible behavior in SmFeAsO0.85 is dominated mainly by normal point pinning (δTc) and surface pinning mechanisms. 相似文献
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利用混合物理化学气相沉积法(hybrid physical-chemical vapor deposition, HPCVD)可以制备出高性能的MgB2超导薄膜, 再对薄膜进行钛(Ti)离子辐照处理.经过辐照处理后的样品被掺入了Ti元素, 与未处理的干净MgB2样品相比,其超导转变温度没有出现大幅度的下降, 而在外加磁场下的临界电流密度得到了明显的提高,同时样品的上临界磁场也得到了提高. 在温度5 K, 外加垂直磁场为4 T的情况下, Ti离子辐照剂量为1× 1013/cm2的样品的临界电流密度达到了1.72× 105 A/cm2, 比干净的MgB2要高出许多,而其超导转变温度仍能维持在39.9 K的较高水平. 相似文献
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Y. Saito T. Inokuchi H. Sugiyama K. Inomata 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):463-469
We conducted a detailed study of hard axis magnetic field (Hhard)
dependence on current-induced magnetization switching (CIMS) in MgO-based
magnetic tunnel junctions (MTJs) with various junction sizes and various
uniaxial anisotropy fields. The decreases in critical current density
(Jc) and the intrinsic critical current density (Jc0) estimated from
the pulse duration dependence on Jc in CIMS are observed when applying
Hhard for all MTJs. The decrease in energy barrier of CIMS is also
observed except for the largest sample. These results indicate that the
reduction of Jc is attributable to both the increase of spin-transfer
efficiency and the decrease in energy barrier in the case of applying
Hhard. The Jc0 decreases with increase in the mutual angle between
the direction of magnetization and the easy axis (θf),
which is consistent with the theoretical prediction proposed by Slonczewski.
The degree of the reduction of Jc0 for the same value of Hhard
decreases with decreasing size of MTJs. This behavior is considered to be
related to not only decrease in θf due to the increase in
anisotropy field in MTJs, but also to the increase in the variance of the
initial angle of magnetization due to the thermally activated magnon
excitation. The stable switching endurance related to CIMS was observed in a
wide range of MTJ sizes when applying Hhard. Moreover, we proposed a new
architecture and a new switching method considering write disturbance. These
results would be useful for application to spin memory and other
spin-electronic devices. 相似文献
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Guchang Han Yugui Wang Hanmin Han Zhihe Wang Shunxi Wang Weifan Yuan Qiaolin Huang Zhiming Liu Jinlin Chen 《Applied Physics A: Materials Science & Processing》1993,57(4):363-366
The transport critical current properties of Bi(2223) silver-clamped thick films are studied by the measurement of its dependence on magnetic field and temperature close to T
c. It is found that the transport critical current follows a power law J
c(1–T/T
c)3/2 for the sample with J
c>2.0×104 A/cm2 (77K, zero field) and that J
c(H) is basically reversible for increasing and decreasing magnetic field. After the transport current exceeds the critical current, the voltage-current (V-I) characteristics show a flux-creep-like behaviour until they smoothly join the flux-flow state. From the measurement of V-I curves, the pinning property of the sample may be estimated using the flux-creep mode. The flux-flow resistance is found to have a nonlinear magnetic field dependence. 相似文献
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We investigated the influence of surface damage on the critical current density (Jc) of MgB2 thin films via 140-keV Co-ion irradiation. The Jc(H) of the surface-damaged MgB2 films was remarkably improved in comparison with that of pristine films. The strong enhancement of Jc(H) caused by a surface damage in MgB2 films can be ascribed to additional point defects along with an atomic lattice displacement introduced through low-energy Co-ion irradiation, which is consistent with the change in the pinning mechanism, from weak collective pinning to strong plastic pinning. The irreversible magnetic field (Hirr) at 5 K for surface-damaged MgB2 films with a thickness of 850 and 1300 nm was increased by a factor of approximately 2 compared with that of a pristine film. These results show that the surface damage produced by low energy ion irradiation can serve as an effective pinning source to improve Jc(H) in a MgB2 superconductor. 相似文献
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Summary Monofilamentary Bi(2223) tapes withJ
c(77 K, 0 tesla) up to 30 000 A/cm2 have been prepared by cold rolling using the powder-in-tube method. An optimization of the precursor powders has led to a
higher phase purity after the reaction heat treatment. The deformation process has been optimized in order to increase the
oxide density and to reduce sausaging effects on the oxide thickness. The transport properties of these tapes have been studied
in a wide range of temperature (4.2K-T
c) and magnetic fields (up to 28 tesla). The critical-current values at 77 K fields of 0.5 T and 1 T parallel to the tape surface
are 10 000 A/cm2 and 5400 A/cm2, respectively. At 4.2 K theJ
c value decreases from 1.6·105 A/cm2 at 0 T to 6·104 A/cm2 at 15 T. At fields higher than 15 tesla a very low field dependence ofJ
c has been found, regardless of the tape orientation. Transport properties have also been studied by cutting small sections
of the tape in order to investigate the local critical-current distribution. It has been found that, even in rolled tapes
of good quality (J
c (77 K, 0 T)>20000 A/cm2), theJ
c distribution is homogeneous: the critical current density increases gradually from the centre of the tape to the sides, the
latter exhibiting much higherJ
c (46000 A/cm2) than in the centre (18000 A/cm2).
Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994. 相似文献
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Soon-Gil Jung W.K. Seong N.H. Lee W.N. Kang 《Physica C: Superconductivity and its Applications》2011,471(21-22):798-800
We have investigated the flux pinning effect of columnar grain boundary in columnar-structured and single crystalline MgB2 films. The MgB2 films with columnar structure showed much higher Jc than that of single crystalline thin film, and sample having smaller grain size had a higher Jc in high magnetic fields. At 5 K, the MgB2 film with grain size of 460 nm showed an abnormal double-peak behavior in pining force density, Fp(B), caused by competition of different types of pinning sites, such as planar defects and point defects. Field dependences of Fp in columnar-structured films suggest that the columnar grain boundary is a strong pinning source in the MgB2 film and it plays a crucial role in enhancing Jc over a wide range of magnetic fields and temperatures. 相似文献
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Y. Yang C.H. Cheng L. Wang H.H. Sun Y. Zhao 《Physica C: Superconductivity and its Applications》2010,470(20):1100-1102
In this paper, we study the doping effect of sorbic acid (C6H8O2), from 0 to 20 wt.% of the total MgB2, on critical temperature (Tc), critical current density (Jc), irreversibility field (Hirr) and crystalline structure. The XRD patterns of samples show a slightly decrease in a-axis lattice parameter for doped samples, due to the partial substitution of carbon at boron site. On the other hand, we investigate the influence of doping on the behavior of flux pinning and Jc(B) in the framework of percolation theory and it is found that the Jc(B) behavior could be well fitted in high field region. The two key parameters, anisotropy and percolation threshold, play very important roles. It is believed that the enhancement of Jc is due to the reduction of anisotropy in high field region. 相似文献
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The quasi-multilayer films of YBa2Cu3O7−δ
/YSZ (YSZ denotes Yttria Stabilized Zirconia) are prepared by means of pulsed laser deposition (PLD), and a systematic study
of the magnetic-field and temperature dependence of the critical current density J
c(H,T) for the YBCO/YSZ quasi-multilayer film is presented. Angular-dependent J
c(H,T) measurements have demonstrated that the growth control strategy is very effective in preventing the vortex motion at high
fields and high temperatures. The temperature dependence of isotropic and anisotropic contribution to J
c is investigated in order to evaluate the strength of the defects. It is suggested that at high applied fields (such as 7
T), the pinning contribution of the YBCO/YSZ quasi-multilayer is dominated by the anisotropic disorders, while at intermediate-low
fields (such as 1 and 3 T) the pinning contribution is determined by both isotropic and anisotropic disorders. 相似文献
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MgB2 coated conductors (CCs), which can avoid the low packing density problem of powder-in-tube (PIT) processed wires, can be a realistic solution for practical engineering applications. Here we report on the superior superconducting properties of MgB2 CCs grown directly on the flexible metallic Hastelloy tapes without any buffer layer at various deposition temperatures from 520 to 600 °C by using hybrid physical–chemical vapor deposition (HPCVD) technique. The superconducting transition temperatures (Tc) are in the range of 38.5–39.4 K, comparable to bulk samples and high quality thin films. Clear (101) and (002) reflection peaks of MgB2 are observed in the X-ray diffraction patterns without any indication of chemical reaction between MgB2 and Hastelloy tapes. From scanning electron microscopy, it was found that connection between MgB2 grains and voids strongly depend on the growth temperature. A systematic increase in the flux pinning force density and thereby the critical current density with decreasing growth temperature was observed for the MgB2 CCs. The critical current density (Jc) of Jc(5 K, 0 T) ~107 A/cm2 and Jc(5 K, 2.5 T) ~105 A/cm2 has been obtained for the sample fabricated at a low growth temperature of 520 °C. The enhanced Jc (H) behavior can be understood on the basis of the variation in the microstructure of MgB2 CCs with growth temperature. 相似文献