高温超导电缆发展的概况

首先讨论了超导体的基本概念、性能和种类。介绍了超导材料研究的进展情况、超导电缆的设计方案、结构和特性参数,并与普通电缆做了比较,最后报道了高温超导线材和导体的结构和特性参数。     

钇系高温超导体中的固相反应

“钇系高温超导体Y-123相通过长时间的低温处理和高压氩离子轰击可以发生固相反应,生成Y-124和Y-125相,同时产生层错等结构缺陷”。这是我们最近使用高分辨电子显微术观察一系列的Y-123高温超导体得出的结论。我们进行这一研究的目的在于为Y-123超导体引入纳米缺陷从而产生钉札作用,达到增强材料临界电流密度的目的。目前钇钡铜氧高温超导体在使用上所遇到的最突出的问题是临界电流密度太低。这主要是因为这些第二类超导体相干长度太短和钉札作用较弱。因此,增强钉札作用可使该材料的临界电     

NaxCoO2（0．75≤x≤1．0）中超结构的透射电镜研究

近期 ,日本科学家Takada等发现了新型层状水合物超导体Na0 3 CoO2 ·1 3H2 O[1] 。该超导体具有层状结构 ,属于强关联体系 ,由于它在导电性和晶体结构上均类似于高温超导体 ,所以引起了科学界的广泛关注。我们用传统的固态反应法得到其母体NaxCoO2[2 ] ,并对其进行了透射电子显微镜研究。图a和b是Na0 75CoO2 的分别沿 [0 10 ]和 [0 0 1]带轴的电子衍射图 ,所有衍射斑点都能准确地指标化 ,分析表明该化合物为六方晶系 ,其空间群为P6 3 mmc ,晶胞参数为a =0 2 8nm ,c =1 0 92nm。图c和d是温度为 10 0K时所拍摄的电子衍射花样 ,显示…     

高JC超导材料磁通分布的电镜研究

在减压降温液氮温区(约64K),采用磁缀饰法(即高分辨Bitter图法),分别在熔融织构生长(MTG)的YBa_2Cu_3O_7超导体和射频溅射制备的单晶外延YBa_2Cu_3O_7薄膜上用KYKY-1000 B SEM观察到超导体的磁通分布图,属无序非晶态结构。在MTG超导体中得到清晰的孪晶界、层界和晶体缺陷对磁通的钉扎图象。最强的钉扎中心出现在尺寸较大的Y_2BaCuO_5(211)第二相粒子周围。     

超导／半导兼容材料的制作及性能分析

介绍了几种结构合理的超导／半导兼容材料的制作技术及其测试结果，重点讨论了超导体（ＹＢＣＯ）与半导体（Ｓｉ，ＣａＡｓ）间缓冲层的选取，并对这几种复合材料的性能作了较详细的分析。     

半导体和超导体混合晶体管的研究进展

半导体和超导体混合晶体管是指以超导体为源极和漏极,半导体为沟道而构成的超导体一半导体混合场效应晶体管(简称混合型场效应晶体管或超导场效应晶体管)和以超导体为基区,半导体为发射区、集电区而构成的超导体-半导体混合结型晶体管(常称超导基区晶体管或超导基区热电子晶体管)。本文将讨论这     

氢与YBa2Cu3Oδ相互作用分析初探

采用正电子湮没技术来初探氢与ＹＢａ２Ｃｕ３Ｏδ超导体中氧空穴和氧的作用，并运用溅射中性粒子质谱仪来检测氢在ＹＢａ２Ｃｕ３Ｏδ中的渗透情况，以了解ＹＢａ２Ｃｕ３Ｏδ中的位错，空穴等微观信息。     

Ti_xY_(1-x)Ba_2Cu_3O_(7-y)的远红外反射光谱

报道了非稀土元素Ti部分替代稀土元素Y的Ti_xY_(1-x)Ba_2Cu_3O_(7-y)(x=0.2,0.4)超导体的远红外反射光谱.观察到至少7个声子结构,分别位于136cm~(-1)、154cm~(-1)(或151cm~(-1))、193cm~(-1)、230cm~(-1)、280cm~(-1)、293cm~(-1)和337cm~(-1)(或345cm~(-1)).结果表明,该超导体的能隙值2⊿≈198cm~(-1),对应2⊿/k_BT_C≈3.4.还对声子结构的物理起因作了探讨.     

合肥研究院超导纳米线研究取得新进展

<正>中国科学院合肥物质科学研究院强磁场科学中心研究员田明亮课题组和张昌锦课题组合作在单晶超导纳米线的超导体-绝缘体转变研究中取得新进展,相关研究结果在线发表在美国化学学会《Nano Letters》上。长期以来准一维超导体的超导—绝缘体转变(SIT)研究一直吸引着很多关注,但是对控制SIT这种转     

超导体的评价实验

<正> 以往,超导体评价实验几乎都是用LHeLN_2杜瓦瓶方法进行的。这种方法,温度控制困难,实验人员必须时刻不离现场测量数据,还要日以继夜地进行实验。现在能够自动进行超导体评价的试验装置已经问世,并在许多研究机构中应用。     

Contribution à la modélisation de lignes hyperfréquences supraconductrices à haute température critique par la méthode FDTD

The purpose of this study is to determine the electrical behaviour of high-Tc superconductor microstrip lines. TheFdtd method is used to put into discrete terms Maxwell’s equations. The two-fluid model has been chosen to describe the behaviour of the superconductor. The variation of electrical parameters such as surface resistance as a function of frequency up to 60 GHz is presented.     

Experimental evaluation of the total shielding current in a bulkhigh-Tc superconductor [YBaCuO]

Total shielding currents of a melt processed bulk high-Tc superconductor (HTS) are evaluated from the measured voltage of a Rogowski coil when a permanent magnet is moved towards the HTS. The total shielding current and the levitation force between the magnet and the HTS show rapid growth and decay depending on the speed of the magnet. The dynamic levitation force and the magnetic relaxation are discussed from the experimental results     

Operation of hybrid current limiter based on high-Tcsuperconducting thin film

A high-Tc superconducting (HTSC) thin film with an inductive shunt was investigated as the model of a hybrid current limiter based on the superconducting-normal state transition. In addition to features previously observed in operation of other current limiters, sharp peaks of rather high frequency were found to appear on the background of a basic low-frequency voltage signal. This is attributed to self-oscillations of temperature and current in the superconductor. The influence of the frequency and magnitude of the circuit current on the character of self-oscillations was experimentally investigated. Qualitative analysis of the conditions for appearance of the self-oscillations under dc and ac conditions was carried out     

Multilayer high-tc superconductor sampler circuit

We designed and measured a high-Tc superconductor sampler circuit based on ramp-edge junctions with an upper-layer groundplane. Undesirable current distributions as a result of parasitic inductance occurred in the circuit. We experimentally observed that about 30% of signal and feedback current distributed to the control line of the read-out SQUID. During sampler operation, we avoided the effect of distributed current by selecting a suitable detection timing for output voltage and we successfully measured a signal current waveform using the circuit at 50 K.     

Flux trapping in a ring-shaped YBCO bulk by pulsed fieldmagnetization

A pulsed magnetic field can be applied using small coils to generate a strong magnetic field for the magnetization of the high-Tc superconductors (HTS) to be used as quasi-permanent magnets in flywheels and motors. The dynamic electromagnetic behavior of two melt-processed ring-shaped Y-Ba-Cu-O bulks using the pulsed field magnetization (PFM) process has been experimentally investigated and analyzed. The flux trapped in the bulk by PFM process was compared to the flux trapped by field cooling process. Both cases then have been analyzed with a numerical model based on the finite-element method (FEM). The power-law model was utilized to relate the electric field to the current density inside the superconductor. The dependence of the critical current density on the magnetic field density was taken into account. Measured and calculated results are compared and discussed     

Response of high-Tc superconductor totime-increasing magnetic field

Using the extended critical state model, we investigate theoretically the magnetic field penetration into a semi-infinite slab of a high-Tc superconductor in the flux flow region when an external magnetic field increases monotonically with time according to power law: H=At^α. The dependencies of the flux flow resistivity and critical current density are taken to depend on magnetic field according to the generalized power law. The behavior of the solutions vs the exponent α and “amplitude” A is analyzed. It is shown that there is the critical value of the exponent α_c separating the regions with different characters of the magnetic field penetration. The value of α_c is determined by the exponents in the dependencies of the superconductor characteristics on magnetic field. For α<α_c, the electric field in a superconductor decreases with time and the magnetic field distribution tends to the one given by Bean’s critical state model. For α>α_c the electric field increases with time and the pattern of magnetic field differs increasingly from Bean’s model; the behavior of a superconductor at large times is described by the model of a normal metal with the resistivity dependent on magnetic field. Thus, the response of a superconductor is described by different approximations on different stages of the process. This result is distinct from that presented in the literature. In the boundary case of α=α_c, the character of the field penetration is time-independent.     

Tunneling spectroscopy: A probe for high-Tc superconductivity

After the pioneering work of Giaever [Phys. Rev. Lett. 5 (1960) 147. [1]] and Shapiro in the 1960s, tunneling spectroscopy has become an important method for studying different properties of superconductors, such as the superconducting gap and the density of states. At the interface with a superconductor there is a variety of tunneling processes depending on barrier properties and the type of materials in both sides of the junction. Among other phenomena, we have single electron (Giaever) tunneling, cooper pairs (Josephson) tunneling [B.D. Josephson, Phys. Rev. Lett. 1 (1962) 251. [17]] and mixed (Andreev-Saint-James reflections [A.F. Andreev, Zh. Eksp. Teor. Fiz. 46 (1964) 1823, Saint-James D., J. Phys 25 (1964) 899]) tunneling. In high-Tc superconductors these phenomena are enriched by the anisotropy of the energy gap, which adds new features, like the so-called ‘Andreev-Saint-James bound states’, which originate the zero bias conductance peak. These peculiarities add to this technique the capability of studying the symmetry of the superconducting gap and the normal state pseudogap. In this report we present a brief review of tunneling spectroscopy applied to high-Tc superconductors and some results about the symmetry of the superconducting gap, supporting the hypothesis of a quantum critical point, which may be at the origin of the superconductive transition.     

Characteristics of millimeter wave detection in a Fabry-Perot resonator using a YBCO-BiO composite superconductor

A quasioptical technique with a hemispherical-type Fabry-Perot resonator for measuring characteristics of millimeter wave detection using a YBCO-BiO composite superconductor has been successfully developed. This Fabry-Perot resonator consists of a spherical mirror and a plane mirror mounted on the cold head of the refrigerator, under a controlled temperature of 40 to 300 K. The method offers the advantages of estimating irradiation power, easily controlling the sample temperature, analyzing the mode of the irradiated millimeter waves and easily extending to higher frequencies. The superconducting millimeter wave detector has been measured with this technique, with measured sensitivities of 46.5 V/W (70 K) to 160 V/W (35 K) at 50 GHz. These results are close to the theoretical values calculated numerically from the characteristics of the detector. It was confirmed that the millimeter wave detection system using the Fabry-Perot resonator is suitable for estimating the sensitivity of the high-Tc superconducting millimeter wave detector.     

Improvement on current limiting performance of current limitingdevices with damping coils

An improved model of the current limiting devices such as the high-Tc superconducting fault current limiter (SFCL) and the reactor have been developed. The high-Tc SFCL mainly consists of the primary copper coil, the secondary high-Tc superconducting rings, and the damping coils, which are magnetically coupled through a three-legged magnetic core. Because a portion of the magnetic flux above the saturation point generated by the fault current is cancelled by the damping coil, thereby the magnetic core is prevented from getting into the saturated state. The limiting current level and the saturation of the core could be controlled by the air-gap length of the central leg with the damping coil. A new design of the SFCL is found to increase the effective impedance by about 60 to 70%, compared to the SFCL design without the damping coils     

Propagation characteristics of high-Tc superconductinginterconnect for VLSI packaging predicted by a generalized two-fluidmodel

A generalized two-fluid model is used to analyze the propagation characteristics of high-Tc superconducting interconnects for very large scale integration (VLSI) packaging. The comparisons for surface impedance of YBa₂Cu₃O_7-x (YBCO) single crystals and thin films show data are in good agreement with the generalized two-fluid model. Based on the generalized two-fluid model, the temperature- and frequency-dependences of the attenuation constant are calculated, the transient responses of a pulse transmitted on a high-Tc superconducting interconnect are simulated, and a simple semi-empirical expression for rise time is given. The results based on the generalized two-fluid model predict an optimum operation temperature range for YBCO interconnect near at liquid nitrogen temperature