实用化Bi系超导带材的制备工艺研究进展

超导材料具备优异的电学和磁学性能,具有很大的发展前景。目前应用最多的是NbTi和Nb₃Sn两种低温超导材料,但是其需要在4.2 K超低温下(液氦制冷)使用,成本高昂。Bi-2223的临界超导温度高达110 K,液氮制冷就可以使用,展现出良好的实用价值。Bi-2223是一种层状结构的化合物,常被制备成带材,使层面方向平行于带材表面,以发挥其最佳超导性能。但是将其实用化过程中还存在着Bi-2223相纯度不高、致密度不够、晶粒连接性不佳、抗拉伸强度和延伸率不足等问题。为了能够实用化,必须兼顾电学性能、机械性能、制冷技术等因素。本文综述了实用化Bi系超导带材的制备工艺与研究进展,分别对Bi-2223前驱粉制备工艺、Bi-2223带材的制备工艺及研究进展、Bi-2223超导带材实用化进展等进行介绍,为其制备工艺和实用化的进一步深入研究提供参考。     

磁场下Bi-2223/Ag异质结的光伏效应研究

在连续紫色激光(λ=405 nm)辐照下,30 K到120 K的温度范围内,对Bi-2223/Ag异质结在0 T到9 T的外加磁场作用下的光伏效应进行了研究.发现60 K和120 K的温度比较特殊,异质结在不同光强辐照下测得的开路电压(Voc)对外加磁场的变化基本无响应.经研究确认在外加磁场的作用下,60 K以下时,Bi-2223/Ag异质结的内建电场源于金属与超导体之间的临近效应.其方向由超导体指向金属银电极.120 K以上时,异质结的内建电场源于金属与超导体之间形成的类P-N结,方向由金属银电极指向超导体.60 K到120 K之间的温度范围内,内建电场源于临近效应和类P-N结两种机制的竞争.     

Bi-2223/Ag异质结的光生电压效应研究

在50 ～ 340 K不同温度下,利用紫色激光(λ=405 nm)对银/铋锶钙铜氧2223异质结界面进行辐照,观测到明显的光生电压效应,发现光生电压的极性分别在超导转变温度TC与320 K附近发生了反转,排除了激光产生的热电势是产生光生电压的原因,分析表明银/铋锶钙铜氧2223异质结界面处存在内建电场:光生电压由异质结界面处的内建电场分离光生电子-空穴对产生的.超导转变温度TC之下以及320 K以上,内建电场方向从超导体指向金属电极;超导转变温度TC与反向温度320 K之间,内建电场从金属指向超导体.     

95;Ar+5;H2气氛退火对Ag/MoS2和Ag/BN/MoS2薄膜形貌和结构的影响

采用射频(RF)磁控溅射在室温下连续逐层沉积,然后在95;Ar+5;H2混合气氛中进行500 ℃低温退火制备了Ag/MoS2和Ag/BN/MoS2纳米薄膜,采用拉曼光谱(Raman)、X射线光电子能谱(XPS)和原子力显微镜(AFM)对其结构、组成和表面形貌进行了研究.结果表明:所制备的纳米膜均匀连续,界面紧密巨清洁.95;Ar+5;H2混合气氛中退火能强烈影响顶部MoS2层的形貌并有效去除MoS2中的杂质氧改善其结晶性、稳定性和结构完整性;顶部MoS2层在沉积态时呈细小颗粒状,退火后呈片层状和颗粒状混合形态,特别是引入BN 层后促进了其向更大更薄的片状转变,巨MoS2薄膜由块状变成类层状结构.另外,电性能表征显示Ag/MoS2具有良好的欧姆接触巨电阻率低,引入BN层使得Ag与BN以及BN与MoS2的界面处产生肖特基势垒从而使Ag/BN/MoS2具有整流特性.     

原位反应合成Ag/CuO复合材料中生成立方氧化铜的研究

本文通过对原位反应合成Ag/CuO复合材料中生成立方氧化铜的可能性进行了研究,对CuO和Ag/CuO分别进行热重-差热分析实验以及反应烧结实验.结果表明:原位反应合成法制备Ag/CuO复合材料中,生成立方氧化铜有三种方式:(1)Cu与O2直接反应合成立方CuO可能性小,或者不发生;(2)以Cu与O2反应合成单斜的CuO后,在后期烧结时发生相转变生成立方CuO为立方CuO的主要形成方式.实验也说明了1048 K(即775℃)左右的温度即是单斜CuO与立方CuO转变的温度;(3)通过实验与理论分析还发现,Ag的存在对形成立方CuO的相变以及形成量有一定的影响.     

原料NiO粉末对燃料电池Ni/SDC阳极材料微结构和性能的影响

分别采用商用氧化镍和煅烧碱式碳酸镍所得氧化镍粉末与Ceo.8Smo.2O2-δ(SDC)粉末混合,经压制烧结制得燃料电池NiO/SDC阳极烧结体,经H2还原后得到Ni/SDC金属陶瓷阳极材料,考察了不同NiO原料和加入量对阳极烧结体和阳极材料的微结构及相关性能的影响,还对以Ni/SDC为阳极构建的燃料电池单电池的性能进行了测试.实验结果表明:煅烧碱式碳酸镍所得NiO粉末和商用NiO粉末的平均粒径分别约为1.1 μm和8μm,前者更为均匀细小;由煅烧碱式碳酸镍所得NiO所制备的Ni/SDC阳极材料具有更高的电导率,含40; NiO的阳极材料(S-Ni/40SDC),在H2气氛中的电导率可达117.5 S·cm-1.以煅烧碱式碳酸镍所得的NiO制备的NiO/SDC为阳极,SDC为电解质,(Y0.5Ca0.5) BaCo3ZnO7-50SDC为阴极的单电池在700℃下的最大输出功率达225 mW/cm2,开路电压为0.85 V,电池性能优于以商用NiO为阳极原料所构建的单电池.     

Pt/Co-N-C电催化材料的制备及其碱性ORR性能

金属有机框架材料(MOFs)是一种制备过渡金属-氮-碳(M-N-C)氧还原电催化材料的有效前驱体，但在热解过程中结构坍塌等问题限制了其实际应用。本研究通过表面活性剂F-127包覆以及Zn掺杂对ZIF-67进行改性，并对改性后的Zn-ZIF-67@F-127在氩气气氛下进行热解，制得结构完整的Co-N-C载体。通过在Co-N-C载体表面进行Pt的负载，制备了Pt/Co-N-C复合氧还原反应(ORR)催化剂，并对其在碱性电解液中的ORR催化性能进行了探究。实验结果表明，F-127的加入提高了Zn-ZIF-67@F-127在热解过程中的形貌保持率，Pt/Co-N-C在O₂饱和的0.1 mol·L^-1 KOH中，催化剂的起始电位、半波电位、极限扩散电流密度分别为1.027 V、0.836 V和5.51 mA·cm^-2,与商用20%Pt/C性能相近。Pt与Co-N-C的协同作用使得催化剂不仅对ORR的四电子路径显示出高选择性，更在计时电流测试中表现出接近于商用20%Pt/C的稳定性与较商用20%Pt/C更优的抗甲醇性能。     

BaFe12O19/Ni0.6Zn0.4Fe2O4复合材料的磁性能研究

采用两步溶胶-凝胶法,分别在850℃,950℃和1050℃下成功制备了BaFe12O19/Ni0.Zn0.4Fe2O4复合材料,利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、振动样品磁强计(VSM)对样品的化学成分、结构、形貌、磁性能进行了表征.结果表明,钡铁氧体大部分呈片状,Ni0.6Zn0.4Fe2O4呈颗粒状分散在钡铁氧体周围.与850℃制备的钡铁氧体和镍锌铁氧体纯相纳米粉体相比,850 ℃制备的BaFe12O19/Ni06Zn04Fe2O4复合粉体的矫顽力和剩余磁化强度介于BaFe12O19和Ni0.6Zn0.4Fe2O4之间;饱和磁化强度(Ms=55.61 emu/g)比钡铁氧体(Ms=53.33emu/g)和镍锌铁氧体(Ms=54.13 emu/g)的都有提高.不同煅烧温度制备的BaFe12O19/ Ni0.6Zn0.4Fe2O4复合粉体,当烧结温度为950℃时饱和磁化强度最大(M =64.84 emu/g);是一种性能优良的磁性材料.     

采用无氟MOD法在织构金属基带上生长YBCO超导薄膜的研究

由于高的使用温度,优良的载流能力以及强的电机械性能,潜在的价格优势,基于YBCO超导薄膜的第二代高温超导带材在电力系统和磁体领域有良好的应用前景.无氟金属有机盐沉积技术具备设备成本低、晶体生长速率快、环境友好等特点,近年来成为了研究制备YBCO超导薄膜技术路线的热点.本文采用FF-MOD技术在CeO2/IBAD-MgO/Y2O3/ Al2O3/Hastelloy C276金属基带上制备200 nm厚的YBCO薄膜,并系统地研究了高温成相过程中BaCO3、YBCO以及YBCO分解相的显微结构及其对超导电性的影响.结果表明,生成的YBCO相晶体呈随机取向,在热处理的过程中逐渐再结晶成为具有双轴织构的YBCO,这与单晶结果相一致.另外,影响YBCO外延形核和生长的关键是控制烧结温度和烧结气氛中的氧分压,抑制BaCO3形成,避免YBCO部分分解.     

泡沫镍负载Ag/MoO2直接电极的制备及其电化学性能

采用水热法制备了不同Ag修饰量的Ag/MoO2纳米复合材料,并利用浸渍法将其负载在多孔泡沫镍(Nickel foam,NF)上制备成Ag/MoO2/NF无粘结剂型直接电极.在该电极中Ag/MoO2纳米颗粒均匀地负载在泡沫镍上形成了三维网络结构,其中MoO2纳米颗粒是由~10 nm的纳米晶组成.当Ag修饰量为5;时,Ag0.05/MoO2/NF具有最佳的电化学性能:在0.1 C的电流密度下,首次放电比容量高达1180 mAh/g,100次循环后仍保持805 mAh/g;且当电流密度由2 C降低至0.1 C时,比容量由468 mAh/g升高至820 mAh/g,表现出优异的储锂性能.     

Crystal structure and superconductivity of Bi-2223

The crystal structure of the Bi₂Sr₂Ca₂Cu₃O_{10 + x} high-temperature superconductor is investigated by the X-ray Rietveld method. The results obtained are used to analyze the structural features of the bismuth high-temperature superconductors in respect to their superconducting properties. The refinement of the structure of the Bi-2223 compound in the four-dimensional space group A2aa (a00) 000 (Z = 4) with the vector q ～ 0.21a* does not reveal any indication of a modulated structure of the Bi-2212 type. The lattice parameters are 5.411(3), 5.409(1), and 37.082(1) Å. The agreement factors are R _wp = 8.10% and R _p = 5.49%. The results obtained are consistent with the notion that bismuth high-temperature superconductors are supercon-ductors with a more distorted crystal structure as compared to other representatives of high-temperature superconductors with critical temperatures T _c > 100 K. These distortions primarily manifest themselves in the segregation of the Bi and O ions of the “charge block” with the formation of zigzag chains that are characteristic of the structure of Bi₂O₃ and are stimulated in particular by defects in the calcium layer.     

Critical aspects on preparation of Bi-2223 glassy precursor by melt-process

It is well known that many Bi–Sr–Ca–Cu–O compositions are glass forming and are converted into high-critical temperature superconductors after proper annealing. Glassy precursors have been prepared by rapid quenching of nominal Bi₂Sr₂Ca₂Cu₃O₁₀ melts from above 1000 °C in air using different conditions. In order to fabricate superconductors having high-critical temperature and current density using the glass–ceramic route, it is necessary to clarify the total chemical composition of the quenched glasses. For the first time the total chemical composition of such melts has been directly investigated by element analysis. The oxygen content has been directly measured by carrier gas hot extraction of as-quenched melts. The investigated cation content in as-quenched nominal Bi₂Sr₂Ca₂Cu₃O₁₀ melts presents significant deviations in composition for the glassy precursor, foremost for the calcium content. The main reasons of the non-complete transition from nominal to obtained composition after the quenching step was showed to be due to inhomogeneous and incomplete melting. This dependency is showed to be highly affected by the nominal composition of the melt. From literature there are barely any published values of the chemical composition of the quenched glassy precursors that would however be critical to control the crystallization behavior and to understand the influences on the superconductive properties.     

Iron stabilization of the 2223 PbBiSrCaCuO superconducting phase

Complete stabilization of crystals of the high-T_c superconducting oxide (PbBi)₂Sr₂Ca₂Cu₃O₁₀, which is characterized by a T_c of 110 K and space group of A2aa, has been achieved by synthesizing the material in an FeO-doped CuO flux. The resulting crystals formed with a chemically inert FeO surface layer appear resistant to further etching or degradation at room temperature and atmosphere.     

On the correlation between solidified microstructures and liquid structural states in Bi-40 wt%Te alloy

The compound-forming alloy Bi-40 wt%Te was selected to explore effects of the temperature-induced liquid–liquid structure transition (TI-LLST) on solidification. The resistivity–temperature pattern of the molten alloy suggested that an irreversible TI-LLST occurred from 694.6 to 723.2 °C as temperature elevated. When solidified from the melt undergoing the TI-LLST, the solidification undercooling of the primary phase Bi₂Te₃ was enlarged and its growth manner was obviously changed, resulting in the spirally curling refined branches, contrary to the orientated thick rod-like crystals solidified from the melt failed to undergo the TI-LLST. Moreover, the volume fraction of the peritectic phase increased from 30.6% to 56.4%, which implied that the phase competition behavior during the peritectic reaction was also changed.     

Voltage‐current characteristics of Bi‐2223 superconducting tape near Tc under γ irradiation

Voltage‐current characteristics at four different applied magnetic fields (7, 20, 30, and 40 mT) of Bi₂Sr₂Ca₂Cu₃O_x superconducting tape were measured in the temperature range from 100 to 115 K. They were also measured at zero magnetic field before and after γ irradiations up to 10 MRad at different temperatures just below the critical temperature. The data were fitted to a power law expression V = I ^β(T) in which the exponential parameter β under 20 mT field and after irradiation is found to fluctuate around three and then drops to unity near the critical temperature which may be interpreted as a sign of Kosterlitz‐Thouless transition. The electrical properties of the tape were found to be very sensitive to γ irradiation where most of the changes take place in low γ doses. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Characterization of Ml2-Intercalated Bi-2212 Cuprates (M=Mn,Fe, Co,Cu, Zn)

Abstract

A series of new layered cuprates with the composition MI_2+xBi₂Sr₂CaCu₂O_8+y (x=0.6–0.9; M=Mn, Fe, Co, Cu, Zn) have been synthesized by the reaction of Bi₂Sr₂CaCu₂O₈ with each transition metal under an atmosphere of iodine at 400°C. The new cuprates, lamellar in shape, are crystallized in a tetragonal unit cell with the lattice parameters of a = 5.393–5.402 Å and c = 43.32–43.96 Å. A structure model for these cuprates are proposed in which the monoiodide anions are intercalated in the Bi₂O₂ layer to form a bilayer accompanying 3d metal cations. All of the intercalated cuprates are non-superconducting to be as high as 0.74–2.52 MΩ · cm in resistivity at room temperature.     

Influence of the VPE parameters on the epitaxial film properties for the (Pb1−xSnx)1+yTe1−y system

Epitaxial films have been produced for 0 ? x ? 1 by steps of 0.1. The growth rate, crystalline quality, carrier concentration and composition have been measured as a function of source, substrate and Te₂ source temperature. The growth rate is adjustable between 0.1 and 36 μm h^-1 and the films have smooth and shiny surfaces. The crystalline quality, conduction type and carrier concentration is mainly determined by the Te₂ pressure. It is possible to choose the type and the carrier concentration in the stable region for a source composition x ? 0.2. The films are always p-type if x ? 0.3. The composition of the films is varied by the source and by the substrate temperature. It is possible to vary the film composition compared to the source composition in the range of ±20% by varying the substrate temperature.     

On the structure of amorphous GexTe1−x systems

Calculations have been made for the quadrupole splitting of a $\text{3}\text{2}$ spin state of Te¹²⁵ in an amorphous Ge_xTe_1?x system. The results favour the existence of a threefold coordinated black phosphorus structure with an excess of TeTe chains for x-values between o and 0.5; beyond 0.5, threefold coordinated GeTe and an excess of amorphous Ge coexist.