Experimental and theoretical approaches for electrical,magnetic, micromechanical,and structural characterization of BSCCO ceramic superconductors

This study investigates how the preparation and re-pelletization of BSCCO ceramic superconductors affects their structural, magnetic, electrical, and mechanical properties. Samples were prepared using conventional methods including the dry solid state (SS) reaction and wet ammonium nitrate (AN) precipitation, with three variations prepared for each technique. The fabricated samples were then characterized with X-ray powder diffraction (XRD) and scanning electron microscopy. The density, resistance vs. temperature characteristics, AC susceptibility vs. temperature characteristics, and magnetic hysteresis properties were measured. In addition, Vicker's microhardness was measured and revealed that all six samples exhibit the reverse indentation size effect (RISE). Microhardness modeling was also conducted. Calculations with Meyer's law, the Hays and Kendall model, and the proportional sample resistance model indicate that the samples are far from the plateau region, whereas the indentation-induced cracking model was consistent with the experimental results. The elastic modulus, Young's modulus, yield strength, and brittleness index were also calculated for each sample.     

The origin of the modulated structure in Sr2CuO3+δ (δ = 0.4): [CuO2] in-plane oxygen vacancy or apical oxygen vacancy?

We propose the question of the modulated structures of copper oxide is caused by the [CuO₂] in-plane oxygen vacancy or apical oxygen vacancy. Sr₂CuO_3+δ single-crystal samples were prepared using high-temperature and high-pressure methods. The major phase of Sr₂CuO_3+δ (δ = 0.4) single-crystal system is found to be constituted by the 5 a modulated structure with the Fmmm space group, which originates from the [CuO₂] in-plane oxygen vacancy appearing in octahedral Cu-O. Besides, the presence of the [CuO₂] in-plane oxygen vacancy may obliterate the superconductivity of the system. Experimental results deduce that the oxygen vacancy may appear in the apical oxygen sites in high-temperature copper oxide superconductors.     

CaCuO2颗粒尺寸对双粉法制备Bi系高温超导带材性能的影响

本文通过基于共沉淀工艺的双粉法制备了Bi_1.76Pb_0.34Sr_1.93Ca_2.0Cu_3.06O_8+d (Bi-2223)前驱体粉末。在这一过程中,首先单独制备了Bi_1.76Pb_0.34Sr_1.93CaCu_2.06O_8+d (Bi-2212)和CaCuO₂(实际相组成为Ca₂CuO₃和CuO)粉末,并分别进行了烧结。通过调节共沉淀工艺过程中的pH值,获得了颗粒尺寸不同的CaCuO₂粉末,然后将Bi-2212与其按照相组成相组成为1:1进行混合,并装入Ag包套中,通过一系列的旋锻、拉拔和轧制工艺,获得设计尺寸的Bi-2223带材。比表面积测试表明随着pH值从3.0增加到5.0和6.5,获得CaCuO₂粉末的平均颗粒尺寸从1.1减小到0.75和0.60 mm。通过扫描电镜对不同尺寸CaCuO₂颗粒制备的Bi-2223生带、第一次热处理和后处理之后带材的相组成和分布进行了表征。结果表明,适当尺寸的CaCuO₂颗粒可以避免团聚现象的出现,因此有利于高载流性能带材的获得。最终通过进一步调节带材的尺寸,1#带材的性能最高,达到了12200 Acm^_-2。     

高场超导磁体研究进展及其应用

高磁场对科学技术的发展具有极其重要的作用,它孕育着许多重大的科学发现和新技术的产生。超高磁场的产生和应用研究对极端条件科学设施、生物医学工程、国防特种装备、高精度的科学仪器以及农业应用都具有重要的意义。目前世界上许多研究机构和实验室开展了基于高温超导带材绕制高场直流超导磁体的项目。本文以高场超导磁体领域几个主要的研究机构为对象,主要介绍其在全超导高场磁体方面进行的研究工作,包括设计方案、技术特点和最新的研究进展,并对高场超导磁体的主要应用进行简要介绍。     

真空管道高温超导侧挂悬浮旋转运动系统改进

侧挂式磁悬浮回转系统拥有两根具有单磁场峰值的永磁轨道。在环形真空管道中,该系统的磁悬浮车可以在6 mm悬浮间隙下达到80 km/h的运行速度。在不大幅改变整体结构的条件下,探讨了一种增大系统运行速度的途径。通过将2个平行的永磁轨道合并成1个具有三磁场峰值的单轨,将显著增强系统的悬浮力,从而有望提高系统的运行速度。然而车体质量的增加将抵消悬浮力增加带来的效应。综合评估二者的影响,结果表明,相比较于具有单磁峰的双轨,具有三磁场峰值的单轨能让系统获得更高的运行速度。并且,对于三磁峰单轨系统,其最大运行速度随超导块数量的增加而增加。相比较于单峰磁轨而言,当超导块列数为17时,三峰磁轨系统的运行速度可以增大8.2%。     

超导无线电能传输技术

近年来,无线电能传输技术已成为了热点技术。与传统电能传输方式相比,无线电能传输更为方便、安全,并已被应用于多个领域。由于无线电能传输效率取决于发射与接收线圈本身的电阻,线圈电阻越小,传输效率越高。超导体所具有的直流零电阻、交流低损耗的特性,使得超导材料用于无线电能传输具有显著的效率优势。介绍了超导无线电能传输技术的研究现状,中国科学院应用超导重点实验室关于超导无线电能传输方面已经开展和正在进行的研究工作,指出了超导无线电能传输技术潜在的应用前景。     

轧制中间热处理温度对Ni7W/Ni12W/Ni7W复合基带组织及织构的影响

采用压延辅助双轴织构技术制备了涂层导体用Ni7W/Ni12W/Ni7W复合基带。复合基带轧制形变过程加入3次不同温度的轧制中间热处理优化其形变组织。采用X射线衍射及背散射电子衍射技术分析了复合基带轧制过程中表面及截面的形变及回复组织,以此探索轧制中间热处理温度对Ni7W/Ni12W/Ni7W复合基带形变及立方织构形成过程的影响机制。结果显示,经600S°C/60Smin轧制中间热处理后的复合基带在较低的再结晶温度下获得了95% (<10°)的高立方织构含量。晶体取向分布图表明该中间热处理温度下复合基带回复及初始再结晶组织中立方取向的晶粒含量都更高;不同取向间点对点的晶体取向差分析证实了立方取向晶粒较大的晶界角,这使立方取向在回复及初始再结晶过程具有高的界面迁移率,从而促进了后续再结晶过程强立方织构的形成。     

Superconductivity in heavily boron-doped silicon carbide

Abstract

The discoveries of superconductivity in heavily boron-doped diamond in 2004 and silicon in 2006 have renewed the interest in the superconducting state of semiconductors. Charge-carrier doping of wide-gap semiconductors leads to a metallic phase from which upon further doping superconductivity can emerge. Recently, we discovered superconductivity in a closely related system: heavily boron-doped silicon carbide. The sample used for that study consisted of cubic and hexagonal SiC phase fractions and hence this led to the question which of them participated in the superconductivity. Here we studied a hexagonal SiC sample, free from cubic SiC phase by means of x-ray diffraction, resistivity, and ac susceptibility.     

Infrared absorption spectroscopy and fluctuations induced conductivity (FIC) analysis of Be-doped TlBa2Ca2Cu3O10−δ superconductor

Be-doped TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ (y=0, 0.25, 0.5, 0.75, and 1.0) superconductor bulk samples were synthesized by solid state reaction and characterized by X-ray diffraction (XRD), dc-resistivity {ρ (Ω cm)}, and Fourier Transform Infrared (FTIR) absorption spectroscopy. Fluctuations induced conductivity (FIC) analysis is carried out on temperature dependent dc-resistivity data of as-prepared and oxygen post-annealed TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ superconductor samples by using Aslamazov–Larkin (AL) and Lawrence–Doniach (LD) models for excess conductivity. Different microscopic parameters such as zero temperature coherence length along c-axis {ξ_c(0)}, inter-layer coupling (J), inter-grain coupling (α), critical exponent (λ_D) and dimensionality of fluctuations are calculated for understanding the role of Be-doping on superconducting properties of TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The cross-over temperature (T_o) is shifted towards higher temperature values with the increase of Be contents in TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The increase in ξ_c(0) and J after Be-doping at Ca sites shows the improvement of inter-plane coupling in TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The increase in zero resistivity critical temperature {T_c(R=0) (K)} up to y=0.5 and then decrease for y=0.75, 1.00 fixed the Be-doping level for optimum increase of superconducting properties of TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The appreciable changes in all the microscopic parameters extracted from the FIC analysis and the increase in relative intensity of almost all the oxygen phonon modes indicate the oxygen diffusion in the unit cell after oxygen post-annealing the samples. The oxygen diffusion can take place at both inter-granular and intra-granular sites, which increase the superconducting volume fraction by improving the grains size, inter-grain connectivity and carrier density.     

Effect of Li doping on the superconducting properties of single domain GdBCO bulks fabricated by the top-seeded infiltration and growth process

Single domain GdBCO bulk superconductors have been fabricated by the top-seeded infiltration and growth process (Gd+011 TSIG) with solid phase compositions of (1-x)(Gd₂O₃+1.2BaCuO₂)+xLi₂CO₃, (x=0, 0.04, 0.08, 0.10, 0.12, 0.16 wt%). The effect of Li₂CO₃ doping on the growth morphology, microstructure, levitation force, trapped field and critical temperature (T_c) of single domain GdBCO bulks have also been investigated based on these samples. The results show that the single-domain GdBCO bulks can be fabricated when x is in the range of 0–0.16 wt%. The size and distribution of Gd211 particles are not influenced by the Li₂CO₃ doping in the samples. The T_c of the samples decrease from 92.5 K (x=0 wt%) to 89.5 K (x=0.16 wt%) when x increases. The decreasing trend of T_c was caused by the substitution of Li⁺ on Cu²⁺ site in the GdBCO crystal. Both of the levitation forces and trapped fields of the samples increase first and then decrease with the increase of x; both of the largest levitation force of 38.5 N（77 K，0.5 T） and the largest trapped field of 0.31 T（77 K，0.5 T） are obtained in the sample when x=0.10 wt%. These results show that appropriate Li doping is an effective way to enhance the flux pinning force and the other physical properties of GdBCO bulk superconductors fabricated by the Gd+011 TSIG method.