BSCCO超导体中均匀排布ZnO缺陷的纳米复合制备

通过纳米复合掺杂的方法,在BSCCO超导体中引入了均匀排布的纳米ZnO缺陷.研究并比较了不同掺杂方法对超导体性能以及ZnO在超导体中分布状态的影响.测试结果表明,不同掺杂方法所制备的样品均有明显的超导现象;经HRSEM表征,纳米复合掺杂所得样品中ZnO缺陷呈线状均匀排布,粒径约为100 nm.     

Fabrication and Electromechanical Characterization of Silver-Clad BSCCO Tapes

The powder-in-tube technique consisting of industrial processes such as wire drawing and rolling has been widely used to fabricate superconducting tapes. In the present investigation a novel technique was adopted to fabricate BSCCO 2223 tapes. Instead of wire drawing, the silver billet was reduced in size by groove rolling. Stress conditions during groove rolling were analyzed and appropriate changes were incorporated to optimize the deformation process. Subsequent thermomechanical treatment resulted in tapes with average critical current densities of 18,000 A/cm². Phase development and microstructural evolution during the thermomechanical treatment were studied using XRD, SEM, and TEM. The electromechanical properties of monofilament and composite BSCCO tapes were evaluated by subjecting them to in situ tensile tests. The strain tolerance of the composite was found to be better than that of the monofilament BSCCO tape.     

纳米晶体光电子性质研究进展

本文综述了近年来国内外纳米晶体光电子性质研究领域某些方面的进展情况，着重介绍了纳米晶体在光吸收、光致发光、非线性光学效应和电导率等方面的独特性能，这些研究表明，对于０￣３ｎｍ晶体（纳米晶粒处于分散介质中）来说，量子尺寸效应是产生晶体光电子性质突变的主要原因之一。对纳米晶体结构和性能的深入研究，能为光电子材料的发展提供新的途径和思路。     

Chemical Stability of the Bi(Pb)-Sr-Ca-Cu-O Superconductors

The changes in volume of superconducting high-T _c (2223) phase of the high-temperature superconductors (HTSC) with nominal composition Bi_3.2Pb_0.8Sr₄Ca₅Cu₇O _x are studied by magnetic susceptibility during soaking of material in water and more aggressive aqueous solutions. The apparent volumes of the 2223 superconducting phase after long-term (168 hr) soaking in H₂O, NaCl_(aq), and NaOH_(aq) decreased to 22%, 17%, and 57%, respectively. The atomic absorption analysis of resulting solutions showed high amounts of Sr²⁺ and Ca²⁺ in H₂O and NaCl_(aq) and lower amounts of Sr²⁺ and Ca²⁺ in NaOH_(aq). The highest content of Pb²⁺ and Cu²⁺ was detected in NaOH_(aq).     

Magnetisation loss of BSCCO/Ag superconducting tape exposed to applied field with arbitrary angle

Bi₂Sr₂Ca₂Cu₃O_x/Ag tape superconductors are used in applications like power cables and transformers. In these applications the superconductor is exposed to an alternating magnetic field that has different orientations with respect to the tape surface. In this paper the angle dependency of the magnetisation loss is considered from two points of view. First the measurement technique with pickup coils is analysed theoretically. Measured magnetisation loss in uni-directional magnetic field with various orientations and rotating magnetic field are compared. When the orientation is changed from perpendicular (0°) to parallel (90°) applied magnetic fields, the contribution of the perpendicular field component to the magnetisation loss is dominant up to 60°. A new model to describe the angle dependency of the magnetisation loss, based on the measured loss in perpendicular and parallel magnetic field is developed. Deviations between models and the measured loss are explained with the help of the theoretical analysis of the measurement technique. The new model is not only applicable for the magnetisation loss but also for other AC loss components.     

Effects of SnO on growth and physical properties of BSCCO whiskers

Abstract

Superconductor whiskers doped with SnO have been fabricated by annealing a melt quenched (Bi₂Sn₁)-223 precursor using suitable heat treatment cycles. Approximately 5 μm thick, 90 μm wide and 5 mm long whiskers were fabricated, and their physical, electrical and magnetic properties were investigated. Crystallisation activation energies of glass phase fabricated were calculated to be 390 kJ mol^–1 using Kissinger method based on the differential thermal analysis data. The T _c value of the whiskers was found to be 94 K from M–T measurement. The magnetisation of whiskers before superconducting transition increased with decreasing temperature, and after superconducting transition, the magnetisation of whiskers decreased, from positive to negative, due to the diamagnetic nature of superconductivity. The change on magnetisation dependence of applied magnetic fields (M–H) showed that whiskers have paramagnetic–diamagnetic multiphase structure.     

Bi-based superconductors prepared with addition of CoFe2O4 for the design of a magnetic probe

We have investigated the microstructure and the magnetoresistivity of bismuth based superconductor bulks added with nano-sized CoFe₂O₄ particles (10 nm in diameter). Samples were prepared through the solid state reaction (SSR) technique by addition of CoFe₂O₄ nanoparticles during the last step of heat treatment. Phase examination using X-ray diffraction (XRD), morphology investigation by scanning electron microscope (SEM), microstructure and local chemical composition analyses using transmission electron microscope (TEM) coupled with energy dispersive X-ray spectroscope (EDXS), electrical resistance versus temperature ρ(T) under applied magnetic fields (B) and electrical resistance versus B at 77 K, ρ(B), were carried out. The CoFe₂O₄ added sample shows a great magnetoresistance to weak magnetic field at the temperature of liquid nitrogen (77 K). This result is attractive for practical, because CoFe₂O₄ added samples can be utilized as active elements in magnetic fields sensor devices.     

锂铁氧体纳米晶的磁性能研究

我们用ＰＥＧ凝胶法合成出的ＬｉＦｅ＿５Ｏ＿３纳米晶，用ＸＲＤ和ＴＥＭ观测其粒径和形貌。用振动样品磁强计考察其比饱和磁化强度σ＿ｓ，随粒径口变化，得到样品的σ＿ｓ随Ｄ的减小而下降。     

Triple Approach to Determination of the c-Axis Penetration Depth in BSCCO Crystals

The c-axis penetration depth _c in Bi₂Sr₂CaCu₂O₈₊ (BSCCO) single crystals as a function of temperature has been determined using three high-frequency techniques, namely (1) measurements of the ac-susceptibility at a frequency of 100 kHz for different sample alignments with respect to the ac magnetic field; (2) measurements of the surface impedance in both superconducting and normal states of BSCCO crystals at 9.4 GHz; (3) measurements of the surface barrier field H_J(T) 1/_c(T) at which Josephson vortices penetrate into the sample. Careful analysis of these measurements, including both numerical solution of the electrodynamic problem of the magnetic field distribution in an anisotropic plate at an arbitrary temperature and influence of defects in the sample has allowed us to estimate _c(0) 50 m in BSCCO crystals overdoped with oxygen (T_c 84 K) and _c(0) 150 m at the optimal doping level (T_c 90 K). The results obtained by different techniques are in reasonable agreement.     

氮化铁纳米晶的溶剂热合成

以氯化亚铁（FeCl₂·4H₂O）为铁源, 氯化铵（NH₄Cl）和叠氮化钠（NaN₃）为混合氮源, 通过溶剂热合成法制备了具有包覆结构的氮化铁纳米晶. 分别采用X射线衍射（XRD)、 透射电镜（TEM)和高分辨透射电镜（HRTEM)对最终产物的形貌特征和物相组成进行了表征, 结合处理前后产物的XRD检测, 探讨了氮化铁纳米晶复合结构形成的机理. 对影响实验的因素,如反应温度、反应时间、加料次序和磁性质等进行了研究. 结果表明：通过严格控制加料次序, 在有机溶剂二甲苯中400℃反应12h可以合成氮化铁复合结构纳米晶. 由于核壳结构的影响, 氮化铁纳米晶最大比饱和磁化强度比文献值低.     

Resistance Behaviour of Nanocrystal Nickel

The resistance behaviour of nanocrystal nickel was studied from 4 to 720 K and 0 to 20 Kbar.A linearvariation of the resistance was found at low temperatures.It showed that under high temperatures,that system transformed to a more stable state,with the relaxation process taking place by stages andinfluenced by exerted pressures.The property,especially the stability,of nanocrystal was closely re-lated to the compacting pressure,     

Texture Characterization of High-Temperature Superconductor Wires

Texture measurements have been made for BSCCO tapes produced by dip coating and by powder-in-tube techniques. The texture of the Bi2212 grains was characterized for both c axis texture using (001) pole figures from 008 reflections and a–b axis texture using (115) pole figures. The critical current densities of these tapes were also measured and correlated with texture parameters obtained from contours of the pole figures. For the tapes with good current transport, the arrangement of grains in a crystallographic sense was inferred from the pole figures and was found to be consistent with a model based on global alignment of the c axes and the presence of colonies of grains differing mostly in c axis twist.     

TI-Ba-Ca-Cu氧化物超导体的微观结构研究

本文研究了Tl-Ba-Ca-Cu氧化物超导体的微观结构与烧结条件的关系,确定了超导相的结晶晶粒的形态特征、元素成分的比例关系,定出了零电阻转变温度为122K的超导相的结构式为TlBa_(1·2)Ca_(0·8)Cu_(1·3)Oy及其X射线的衍射数据。     

Numerical study on self-field losses of 30 m BSCCO HTS transmission cable

The self-field losses of the one phase of high-T_C superconducting (HTS) transmission cable are calculated by the electric circuit (EC) model. The one phase of HTS cable is constructed by the former of fine-strands copper rod, HTS conductor with four superconducting layers, the insulation made by polypropylene laminated paper, and HTS shielding with two superconducting layers, which was fabricated by Sumitomo Electric Industries (SEI). The length of the cable is 30 m. Each HTS layer comprises BSCCO tapes. The current-dependent resistance of HTS layers in EC model is estimated on the base of Norris expressions for ellipse. The calculated losses are compared with the experimental results measured by 4-terminal method by SEI. The calculation of alternating current (AC) losses, a summation of the self-field losses in HTS layers and the eddy-current losses in the former, is almost equal to the measurement at wide transport-current range below the lowest value of the layer critical current. This result indicates that the numerical calculation by EC model is quite reliable. The minimum AC loss is also calculated by obtaining the optimum helical-pitch lengths of HTS layers at transporting 1 kA_rms. The minimum loss is 36% lower than the loss of HTS cable designed by SEI at the transport current value. In HTS cable with the optimum helical-pitch lengths, the calculation of the layer currents are not uniform in HTS conductor but are almost uniform in HTS shielding, which is contradict to SEI’s one. It is considered that the numerical calculation by EC model is useful to obtain the optimum helical-pitch lengths in HTS cable with the minimum AC loss.     

Surface Dependence of Protein Nanocrystal Formation

The self‐assembly kinetics and nanocrystal formation of the bacterial surface‐layer‐protein SbpA are studied with a combination of quartz crystal microbalance with dissipation monitoring (QCM‐D) and atomic force microscopy (AFM). Silane coupling agents, aminopropyltriethoxysilane (APTS) and octadecyltrichlorosilane (OTS), are used to vary the protein–surface interaction in order to induce new recrystallization pathways. The results show that the final S‐layer crystal lattice parameters (a = b = 14 nm, γ = 90°), the layer thickness (15 nm), and the adsorbed mass density (1700 ng cm^?2) are independent of the surface chemistry. Nevertheless, the adsorption rate is five times faster on APTS and OTS than on SiO_2, strongly affecting protein nucleation and growth. As a consequence, protein crystalline domains of 0.02 µm² for APTS and 0.05 µm² for OTS are formed, while for silicon dioxide the protein domains have a typical size of about 32 µm². In addition, more‐rigid crystalline protein layers are formed on hydrophobic substrates. In situ AFM experiments reveal three different kinetic steps: adsorption, self‐assembly, and crystalline‐domain reorganization. These steps are corroborated by frequency–dissipation curves. Finally, it is shown that protein adsorption is a diffusion‐driven process. Experiments at different protein concentrations demonstrate that protein adsorption saturates at 0.05 mg mL^?1 on silane‐coated substrates and at 0.07 mg mL^?1 on hydrophilic silicon dioxide.     

Critical Current Anisotropy of Tl-1223 Superconductors

A comparative study of the critical current anisotropy of Tl-1223 conductors manufactured by different techniques, prepared from different compositions and originating from different research laboratories is presented and discussed. For highly oriented layers, with the magnetic field (B) parallel to the ab plane, the normalised critical current density (j) versus magnetic field characteristic shows very little drop of j value due to the intrinsic properties of the Tl-1223 phase, while all powder-in-tube conductors show a rapid drop of j value in fields as low as 10 mT. For all powder-in-tube conductors the anisotropy coefficient k shows a very pronounced minima at fields up to 30 mT followed by a monotonic decrease of anisotropy with increase of the magnetic field. This is due to poor grain alignment and a demagnetising effect in the powder-in-tube Tl-1223 tapes.     

Distinctions Between Classes of Superconductors Involve Their Degree of Structural Connectivity

A distinction is made between extreme types, such as highT _c cuprates and soft-metal superconductors concerning the extended, relatively exchange frustration-free covalent ring structures (eight-membered) in the former. Phenomenology indicates for cuprates that bond order (BO) effects within a given number of doped bonds can create real space organization of pairs around O super-exchange centers (trijugate position) within a mobile pair kernel. Indications for this postulated new quantum chemical principle have now been found in related electronic crystal behavior by STM. This situation creates small coherence lengths (∼4 atoms) and unusually high pair numbers. For optimal doping, all holes are converted into pairs and these pairs show trends to geometric checkerboard patterns due to characteristic charge-lattice lock-ins, such as configurations withh _op=0.25 orh _op=0.16. Period of BO and the degree of isolation of the planes determineT _c. Doping curves reflect BO events and are roughly predictable from structural data alone. It is suggested that a variety of related materials with large member rings (e.g. C₆₀) follow the relevant BO phenomenology. By contrast, soft metal superconductors (e.g. Pb) are based on 3D close packed structures with small triangular rings in which exchange interactions are frustrated and small. “Normal” BCS isotope effects suggest the operation of phonons in pair formation over extended coherence lengths (>100 atoms). Very small pair numbers are created through phonons.     

金属纳米晶的制备及其在MOS电容结构中的存储特性

优化了金属纳米晶的制备工艺参数,得到了分布均匀,形状为球形,平均尺寸8nm,密度2.5×1011/cm2的Ag纳米晶.在此基础上,制备了包含Ag纳米晶的MOS电容结构.利用高频电容-电压(C-V)和电导-电压(G-V)测试研究了其电学性能,证明该MOS电容结构的存储效应主要源于金属纳米晶的限制态.电容-时间(C-t)测试曲线呈指数衰减趋势,保留时间290s,具有较好的保留性能.     

分光光度法测定Fe-Si-B-Nb-Cu合金中的铌含量

应用分光光度法对Fe-Si-B-Nb-Cu合金中铌含量的测定进行了研究。对试样的预处理方法、试剂和显色剂的加入量以及显色时间与温度等条件进行了优化。在优化条件下,于650nm波长处对试样进行比色分析。实验结果表明,该方法测定结果与电感耦合等离子体发射光谱法测定结果相符,其回收率为94.0%～99.5%,测定结果的相对标准偏差小于1.0%(n=11),该方法操作简便、分析成本低,能满足纳米晶合金中铌含量的测定精度。     

Constancy of the Surface Energy during the Melting of a Nanocrystal

The relation for the surface free energy @sgr; as a function of size and shape of a nanocrystal is derived. The nanocrystal has the form of a parallelepiped with a square base. The ratio of the lateral edge length to the base edge length f defines the shape of a system. It is shown that the value of @sgr; decreases with degreasing number of atoms N in a nanocrystal. The higher the deviation of the form parameter f from unity, the stronger the dependence @sgr;(N). It is found that the surface free energy decreases with the temperature T; in so doing, the quantity (d/T) is the greater, the smaller the size of the nanocrystal or the greater the deviation of the nanocrystal shape from the most thermodynamically stable, cubic, shape. It is shown that the nanocrystal melts when its surface energy decreases to a certain value independent of size and shape. The conditions are discussed under which the crystal fragmentation and dendritic growth are realized.