Cu含量变化对Bi-2212高温超导材料相演变过程及超导性能的影响

采用共沉淀工艺制备了不同Cu含量的Bi-2212前驱体粉末,并通过分步烧结工艺对前驱体粉末中Cu含量不同所引起的相演变过程的变化进行了系统的分析。结合浸涂法和粉末装管法制备了Bi-2212厚膜及单芯线材。研究结果表明,Cu含量的变化对厚膜和带材在烧结过程中的相演变过程同样具有极大的影响。随着Cu含量的增加,体系的相演化过程发生了改变。最终材料中Bi-2201相的含量逐渐减少,而AEC相的含量逐渐增加。考虑到Bi-2201和AEC对载流过程的影响各不相同,通过系统的优化,获得了最佳Cu含量为x=2.2。在这一成分处,厚膜和单芯带材临界电流密度同时达到最大值。     

SOLIDIFIED PRODUCT FROM Bi-Sr-Ca-Cu-O MELT AND ITS TRANSFORMATION INTO SUPERCONDUCTOR

The Bi_2(Sr,Ca)_3Cu_2O_x system superconductor was prepared by different melting proceduresand after treatment.The effects of cooling rate,annealing temperature and time,as well asmelting procedures on phase transformation were investigated.The structure and propertieswere examined by X-ray diffraction,optical microscopy,EPMA,DTA,TGA andmeasurements of electric and magnetic properties.When the melt of nominal compositionBi_2(Sr,Ca)_3Cu_2O_x solidified in air,the Bi_2(Sr,Ca)_3Cu_2O_(8+δ)(2212)superconducting phase isstable,the easily solidified product including Bi_2(Sr,Ca)_2CuO_(6+δ)(2201)phase is metastable,and another may be amorphous if rapidly quenched.The last two may transform into 2212phase by after treatment at an optimal annealing temperature ranging 780—870℃.While2201 phase,prepared by the laser floating zone melting method,may easily transform into2212 phase at layer or filament in shape which is favourable to improve the links amongsuperconducting grains and critical current density.     

EPR studies of (Bi, Pb)-2223 phase substituted by Ruthenium ions

This work studied X-ray powder diffraction (XRD), electrical resistivity and electron paramagnetic resonance (EPR) measurements for Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−xRu_xO_10+δ (0.0 ≤ x ≤ 0.4) superconducting samples. XRD analysis and electrical resistivity data showed that the low-content of Ru, x ≤ 0.05, enhanced both the phase formation and the superconducting transition temperature of (Bi, Pb)-2223 phase. A phase change from (Bi, Pb)-2223 phase to (Bi, Pb)-2212 phase was reported for x ≥ 0.15. Two EPR lines were observed for 0.0 ≤ x ≤ 0.075, indicating the presence of both (Bi, Pb)-2223 and (Bi, Pb)-2212 phases. While, one EPR line was observed for x ≥ 0.15, corresponding to the (Bi, Pb)-2212 phase formation. The number of spins (N) participating in the resonance and its spin paramagnetic susceptibility (χ), for the two phases, were calculated as a function of both Ru-content and temperature. In addition, we reported the variation of activation energy (E_a), Curie constant (C), Curie temperature (θ) and effective magnetic moment (μ) with Ru-content.     

GROWTH OF Bi(Pb)-Sr-Ca-Cu-O SUPERCONDUCTING WHISKERS

Amorphous Bi(Pb)-Sr-Ca-Cu-O strips of types(1112)and(2212)were made by means ofnon-equilibrium solidification of melt-quenching method,On the surface of glassy strip,theflexible(2212)superconducting whiskers have been obtained.The growth and feature ofsuperconducting whiskers were studied in detail.     

铋系超导线材拉拔过程中的粉体变形行为

单芯和多芯拉拔工艺是铋系高温超导带材(Bi-2223/Ag)制备过程中必不可少的重要环节。为研究超导粉体在拉拔过程中的变形行为,对单芯超导线材的拉拔工艺进行理论分析,建立了工艺参数与粉体密度之间的关系,并通过试验验证其合理性。同时,采用大截面减缩率单芯拉拔工艺来实现铋系超导线材的节能高效成形。对1.86mm61芯Bi-2223/Ag线材进行显微硬度测试,并结合数值模拟进行三道次拉拔加工,分析认为:在加工过程中,各超导芯之间及芯内部均存在密度分布不均匀性,且各层粉体密度随拔制过程不断波动,将不利于后续轧制工艺。为此,提出渐进跑道形三道次拉拔工艺,并应用于铋系超导带材的后期拉拔加工,可提高最终带材的临界电流密度10.1%。     

复合Bi系超导多芯带材轴向荷载作用下的临界电流退化模型与分析

超导材料由于在外部载荷作用下表现出的超导性能退化效应严重制约了其工程实际应用。基于脆性纤维金属基增强复合材料损伤理论,应用Weibull分布函数建立了轴向荷载作用下的复合多芯Bi系超导带材的力学变形对临界电流影响的退化模型。给出了轴向加载和卸载过程超导带材临界电流随轴向应变的变化关系;并对超导带材不同初始损伤以及预应变情形下的临界电流随轴向应变的变化关系和退化进行了理论预测,能够给出与实验结果吻合良好的轴向应变对临界电流的退化影响。     

Bi系高温超导体中非公度调制结构相的空间群测定

采用会聚束电子衍射 (CBED) 对Bi--2212相和Bi--2223相中具有非公度调制结构的超胞结构进行了测定. 测定结果表明: 具有 A型调制结构Bi--2212相超胞的点群是2mm, 空间群是I2mm; 具有B型调制结构Bi--2223相超胞的点群是mmm, 空间群是Ibmm. 结合实验结果讨论了摇摆曲线对CBED图对称性的影响, 并指出: 采用CBED测定晶体结构的对称性时, 应以高阶Laue线为依据, 而不应依 靠0层盘内摇摆曲线的对称性. CBED图模拟结果表明: Bi--2212相CBED图显示的是调制结构超胞的对称性, 而不是亚胞的对称性.     

Effect of cooling rate on evolution of superconducting phases during decomposition and recrystallization of (Bi,Pb)-2223 core in Ag-sheathed tape

The reformation of (Bi,Pb)-2223 from the liquid or melt is very important for a melting process of (Bi,Pb)-2223 tape. By combination of quenching experiment with X-ray diffraction (XRD) analysis, the effect of cooling rate on the evolution of three superconducting phases in the (Bi,Pb)-2223 core of Ag-sheathed tape was investigated. The results show that (Bi,Pb)-2223 reformation from the melt seems to experience different routes during slowly cooling at different rates. One is that (Bi,Pb)-2223 phase reformed directly from the melt, and no Bi-2212 participate in this process. The other is that (Bi,Pb)-2223 is converted from the intermediate product, Bi-2212, which formed from the melt during the first cooling stage. Due to the inherent sluggish formation kinetics of (Bi,Pb)-2223 from Bi-2212, only partial (Bi,Pb)-2223 can finally be reformed with the second route.     

Fabrication of non-superconducting and superconducting joints of Ag/Bi-2223 tapes by diffusion bonding

Diffusion bonding of multifilamentary Ag/Bi-2223(Bi_2Sr_2Ca_2Cu_3O_x) superconducting tapes has been performed successfully.Three types of joints,namely,with silver interlayer (type I),bonded directly (type II),with Bi-2212(Bi_2Sr_2Ca_1Cu_2O_x) powder interlayer or with Bi-2223 powder interlayer (type III) were researched,respectively.The critical currents(I_C) of these joints were measured and microstructures of the joints were evaluated by scanning electron microscope (SEM).The result shows that type I is non-superconducting joint with very low resistance,and type II joint and type III (with Bi-2212 or Bi-2223) joints are both of superconducting property.By comparing,type II joint possesses most excellent superconductivity,type III joint with Bi-2223 powder interlayer takes the second place,and type III joint with Bi-2212 powder interlayer is least.     

前驱粉的相组成对Bi（Pb）-2223／Ag带材的微观结构和性能的影响

通过改变粉末的最终烧结温度制备出不同相组成的前驱粉。研究了前驱粉的相组成对Bi(Pb)-2223／Ag带材性能和带材微观结构的影响；从而得出装管前粉末的最佳相组成为：(Pb)2212主相加上一定量的第二相[Ca2PbO4和(Sr，Ca)CuO]，不含2201和2223相。前驱粉的最佳烧结温度应刚好低于2223相的起始成相温度820℃。制备出的最高带材性能Jc达到12kA／cm^2。     

钛基复合材料的红外渗透和连接

迄今人们在Ｂｉ系超导体粉末制备中尝试和应用过的方法有：传统的固态反应法，溶液自蔓延高温合成法，共沉淀法，溶胶－凝胶法，冰冻干燥法，溶剂蒸发法以及微乳胶基粉末合成法，本文详细论述了这些方法的原理、优缺点及其在Ｂｉ系超导体粉末制备中的应用。     

Melt processed YBa2Cu3O7−x superconductors

The superconducting YBa₂Cu₃O_7−x samples were prepared by an Arc-Cast-Annealing (ACA) and Arc-Quench-Powder-Growth (AQPG) processes as modifications of QMG and MPMG techniques. Pe'lets of YBa₇Cu₃O_7−x were quenched by arc-casting in a water cooled copper mould and then the solidified rods were annealed at different temperatures and times to store the superconductivity. Annealed at an appropriate temperature the cast rods showed rising superconducting properties with increasing the annealing time. Some of the rods after solidification were crushed to give powder which was compacted and then subjected to a melt growth process. As a result of this processing, large grained textured YBCO superconductors with dispersed 211 inclusions in the superconducting grains were produced. The microstructure and physical properties of these ACA and AQPG samples were investigated when subject to various temperature cycles. It was found that the volume fraction and size distribution of the second phase inclusions were dependent upon the maximum temperature during the melt growth process. The critical current density (J_c) for ACA and AQPG samples was estimated from magnetization loops using Bean's critical state model. It was found that the value of J_c of AQPG sample was much higher than that of ACA sample.     

高2223相含量粉末扩散连接BSCCO带材

采用压制和高温烧结工艺获得了2223相含量达88.5%的粉末中间层,压制工艺有利于提高粉末中2223相的含量.用上述粉末实现了61芯BSCCO带材的超导扩散连接.结果表明,当连接温度为800℃、保温时间为2 h及压力为3 MPa时,接头平均超导连接效率CCRo可到达49.9%;粉末中2223相含量增加,接头连接效率提高.连接参数对接头显微组织的影响既明显又复杂.     

The effect of f-ion valence on superconductivity in the series Pb2Sr2RCu3O8 (R=Ce, Pr, Tb and Am)

The magnetic properties and valences of the rare earth ions are probed in the superconducting series Pb₂Sr₂R_1−xCa_xCu₃O₈ (R=Ce, Pr, Tb and Am). The R=Pr and Tb samples are superconducting for x≈0.5 below 61 and 72 K, respectively, whereas the Ce and Am samples could not be made superconducting for any single phase sample, irrespective of x. X-ray absorption near edge spectroscopy (XANES), used to probe the valence of R, reveals that Pr and Tb are trivalent whereas the Ce and Am are tetravalent. This direct correlation of R valence and the observation of superconductivity is discussed.     

Na掺杂对Bi-2212高温超导体性能影响研究

本文采用放电等离子烧结(SPS)工艺制备了Na掺杂的Bi_2.1Sr_1.96Ca_1-xNa_xCu_2.0O_8+d超导材料。Bi-2212前驱体粉末采用改进的共沉淀工艺制备,并在烧结前将前驱体粉末与NaOH混合。本文系统研究了Na离子掺杂对Bi-2212体系晶格结构、相组成、微结构和相关超导性能的影响。Na离子掺杂导致Bi-2212体系相转变温度的显著降低。因此在SPS过程中,烧结温度相应发生了变化。但Na掺杂仍然导致大量Bi₂Sr₂CuO₆ (Bi-2201)相生成,进而导致了超导相含量的降低和织构度的破坏,所以给体系的超导电性带来了负面的影响。另一方面,Na掺杂相Bi-2212中掺入了大量的点缺陷,这些点缺陷可以作为有效钉扎中心。因此,通过优化Na掺杂Bi-2212的烧结工艺,有可能在高场条件下获得体系性能的改善。     

部分熔化处理工艺对（Bi，Pb）-2223／Ag带材相组成和微结构的影响

通过部分熔化处理工艺和普通两段热处理工艺的对比研究，分析了部分熔化处理工艺在不同热处理阶段对(Bi，Pb)-2223/Ag带材相组成和微结构的影响。实验结果显示，在熔化温度下，部分(Bi，Pb)-2212相发生分解，分解为(Sr,Ca)2CuO3相、(Sr，Ca)Cu2O3相和富(Bi，Pb)液相，与此同时(Sr,Ca)2CuO3相和(Sr，Ca)Cu2O3相快速长大。随着冷却和成相处理，(Sr,Ca)2CuO3相和(Sr,Ca)Cu2O3相长大到一定尺寸，各相系统达到平衡后，就不再长大，并和部分液相反应，重新生成具有良好取向的(Bi，Pb)-2212相。在成相处理阶段，(Bi，Pb)-2212相转化为(Bi，Pb)-2223相，同时生成的(Bi，Pb)-2223相继承了(Bi，Pb)-2212相的良好取向，使(Bi，Pb)-2223相织构得以改善，致密度得到提高，结果最终带材的性能得到提高。通过部分熔化处理工艺处理的带材Ic达到51A，而普通两段热处理工艺处理的带材Ic为36A，Ic提高了约40％。     

TEM Study on the Ag-BSCCO Interface of Silver-sheathed Bi-2223 Superconducting Tape

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不同厚度Tl-2212薄膜的表面形貌及超导特性研究

采用直流磁控溅射法和后退火技术在蓝宝石基片上制备了Tl-2212超导薄膜,考察了Tl-2212薄膜的厚度对其形貌和超导特性的影响。实验结果表明,随着超导薄膜厚度增加,其表面形貌由致密平整的结构演化为片状晶体结构,临界转变温度Tc和临界电流密度Jc先增大后减小,微波表面电阻Rs先减小后增大。在退火的CeO2缓冲层上所制备的无裂纹薄膜的最大厚度达到600nm,并仍然具有良好的超导性能。     

Optimization of Partial Melting Process for Bi-2212 Multi-Filament Wires

采用共沉淀工艺制备Bi-2212前驱体粉末,并结合粉末装管法得到19×(36+1)的Bi-22212多芯线材。在部分熔化热处理过程中分别对最高热处理温度Tmax和冷却速率Rc1进行了优化。使用扫描电子显微镜对线材中第二相的分布和芯丝状态进行观察。同时,通过对线材进行差热和热重等热分析方法,对线材在热处理过程中的气孔和第二相的形成过程进行定量分析。结果发现,最高热处理温度和冷却速率对芯丝中包括Bi-2201和AEC等在内的第二相种类和含量,及气孔密度都有较大影响。最终获得最优化的热处理工艺为Tmax=892℃,并且冷却过程采用Rc1=40℃/h的两步降温法,在77 K自场条件下得到了4400 A·cm-2的临界电流密度,本研究为进一步提高Bi-2212线材熔化热处理过程优化提供了理论依据。     

熔化处理温度对银包套带材中（Bi，Pb）-2223相熔化分解-再形成行为的影响

应用X射线衍射（XRD）和扫描电镜／能谱分析（SEM／EDS）研究了7．5％O2-Ar条件下，熔化处理温度对银包套单芯带材芯部（Bi，Pb）-2223（简称2223）相的分解及再形成行为的影响。结果表明，适当温度下，2223相部分熔化生成一种类似于（Bi，Pb）-2212的液相和碱土铜酸盐（AEC），主要是（Sr，Ca）14Cu24O41（14：24-AEC）和（Ca，Sr）2CuO3（2：1-AEC），对于这一高温超导相的可逆再形成至关重要。随着熔化处理温度的升高，2223相熔化分解生成的液相的成分经历了从介于2223和2212计量比之间向2212，并进一步向2201计量比的演变过程。2223相易于从类似于2212的液相中析出，而从接近2201计量比的液相中更易于生成2212相。2223相从过度熔化生成的液相中再形成经历了两个途径：一是直接从液相中析出，二是由冷却过程初期形成的2212相转变而来。