钛酸锶衬底表面改性对YBCO高温超导薄膜性能的影响北大核心CSCD

YBa_2Cu_3O_(7-x)(YBCO)高温超导材料在高温高场中具有比较高的临界电流密度,因此具有较好的应用前景.通过研究YBCO高温超导薄膜,以提高它的载流能力和超导性能是市场应用的迫切需要.文中所研究的钛酸锶(SrTiO_3)衬底,作为一种钙钛矿结构,不仅具有良好的化学和热稳定性,而且与YBCO高温超导薄膜具有较小的晶格失配度.通过酸腐蚀法和无酸腐蚀处理钛酸锶SrTiO_3(100)(STO)衬底,运用原子力显微镜观察了两种衬底处理方法对钛酸锶衬底表面结构的影响.并在其上用三氟乙酸盐金属有机沉积法(TFA-MOD)制备出临界密度达到约2.50~3.00 MA/cm^2的YBCO高温超导薄膜.通过四引线法表征YBCO高温超导薄膜的Tc达到了均约93K.通过扫描电子显微镜(SEM)分析了衬底处理技术的不同对其表层生长的YBCO高温超导薄膜形貌的影响.通过X射线衍射仪(XRD)固定方位角法表征了不同的衬底处理技术对薄膜内的残余应力的影响.     

钛酸锶衬底表面改性对YBCO高温超导薄膜性能的影响

YBa_2Cu_3O_(7-x)(YBCO)高温超导材料在高温高场中具有比较高的临界电流密度,因此具有较好的应用前景.通过研究YBCO高温超导薄膜,以提高它的载流能力和超导性能是市场应用的迫切需要.文中所研究的钛酸锶(SrTiO_3)衬底,作为一种钙钛矿结构,不仅具有良好的化学和热稳定性,而且与YBCO高温超导薄膜具有较小的晶格失配度.通过酸腐蚀法和无酸腐蚀处理钛酸锶SrTiO_3(100)(STO)衬底,运用原子力显微镜观察了两种衬底处理方法对钛酸锶衬底表面结构的影响.并在其上用三氟乙酸盐金属有机沉积法(TFA-MOD)制备出临界密度达到约2.50~3.00 MA/cm~2的YBCO高温超导薄膜.通过四引线法表征YBCO高温超导薄膜的Tc达到了均约93K.通过扫描电子显微镜(SEM)分析了衬底处理技术的不同对其表层生长的YBCO高温超导薄膜形貌的影响.通过X射线衍射仪(XRD)固定方位角法表征了不同的衬底处理技术对薄膜内的残余应力的影响.     

电镀铜对YBCO超导带材临界电流影响的研究

钇系超导带材(YBCO)由于载流能力强、不可逆场高,是近年来高温超导材料领域的研究热点,并在电力行业实现示范应用。YBCO超导带材由基底、缓冲层、超导层和保护层组成,可通过电镀铜工艺实现保护层的制备。目前,有关电镀铜对YBCO超导带材临界电流的影响还鲜有报道。因此,本研究对比了镀铜前后YBCO超导带材的表面形貌和临界电流。实验结果表明:电镀铜在提高带材机械强度的同时,对其超导电性并无明显影响。     

低氟MOD法制备YBCO及其银掺杂效应

金属有机溶剂法(MOD)是制备高质量YBCO涂层导体的主要方法之一.银掺杂可以有效降低晶界的弱连接改善薄膜的表面形貌,提高涂层导体的超导性能.目前,主要以物理方法和块材为主。本文采用低氟MOD方法进行银掺杂,在哈氏合金缓冲层上制备了YBCO-Ag,首先研究了银对YBCO织构的影响,然后研究了银对YBCO成相温区的影响。实验结果表明银掺杂可以抑制a轴成核,YBCO-Ag在较宽的成相温区具有良好c轴织构,样品表面平整致密无裂纹.     

YBa2Cu3O7-δ/LaAlO3和Tl2Ba2CaCu2O8/LaAlO3高温超导薄膜内的应变对其微波表面电阻影响的研究

YBa2Cu3O7-δ/LaAlO3 (YBCO/LAO) 超导薄膜是通过热蒸发沉积方法制备的,实验中使用的Tl2Ba2CaCu2O8/LaAlO3 (TBCCO/LAO) 超导薄膜是通过直流磁控溅射方法制备的.通过分析两片超导薄膜的XRD谱计算出了两片超导薄膜内的应变,ΔCY=4.8483×10-3;ΔCT=8.5272×10-5,结果显示YBCO超导薄膜内的应变要大于TBCCO超导薄膜内的应变.另外,采用共面谐振技术研究这两片超导薄膜内的微波表面电阻随温度的变化,结果表明YBCO超导薄膜具有更大的微波表面电阻.分析和讨论了应变对超导薄膜微波表面电阻的影响.     

预处理气氛对电子束蒸发制备YBCO薄膜性能和结构的影响

采用先电子束沉积后退火的两步法制备YBCO超导薄膜;根据薄膜的超导临界电流密度、X射线衍射(XRD)和扫描电镜(SEM)的测试结果,研究了不同预处理气氛对YBCO薄膜结构、表面形貌及超导性能的影响。     

反应共蒸发法REBa_2Cu_3O_(7-δ)薄膜的异位成相过程研究

REBa_2Cu_3O_(7-δ)高温超导涂层导体是当前液氮温区载流能力最强的超导材料,它在大科学装置、军事国防、电力传输、磁悬浮列车等领域具有广泛应用潜力.按照薄膜沉积方式和成相步骤,超导层的制备技术路线可分为原位法(In-situ)和异位法(Ex-situ).本文将对异位法中的反应共蒸发法(RCE Reaction Co-evaporation)制备REBCO薄膜的物相形成规律进行研究,明确超导薄膜及其涂层导体在纳米级前驱组分、晶化温度调制下而形成的不同于块体体系的物相关系、织构生长特征.通过不同氧处理条件薄膜的组分和结构表征,获得了成相过程特征,发现较短的氧处理时间,"富稀土元素"组分等工艺设计有助于薄膜超导成相和c轴织构的形成.正REBa_2Cu_3O_(7-δ)(REBCO,RE=Y,Gd等稀土元素)高温超导涂层导体因其可克服晶界弱连接,高密度位错缺陷,进而提供强磁通钉扎且在液氮温区具有较高的载流能力和不可逆磁场成为倍受关注的热点材料.超导层的快速制备、厚膜织构的有效控制、磁场下的高临界电流密度以及制造成本的降低是第二代高温超导带材发展的关键问题[1-3].如今二代高温超导带材制备技术日趋成熟,主要分为物理法和化学法两大类[4],而按照其前驱膜     

Y_2O_3缓冲层对YBCO超导转变温度的影响（英文）

超导薄膜所受的应力对其临界转变温度Tc具有重要的影响,研究应力对超导薄膜Tc的影响对获得更高Tc材料具有重要意义.本文采用溶胶-凝胶法,在LAO单晶基板上制备了Y2O3/YBCO薄膜,并研究了Y2O3缓冲层对不同厚度YBCO超导薄膜的临界转变温度的影响.研究发现,当YBCO薄膜厚度为90nm时,由于Y2O3和YBCO薄膜的晶格错配,在YBCO/Y2O3薄膜的a-b面内引入了压应力,增加了c轴的晶格常数,结果提高了YBCO薄膜的临界转变温度.当YBCO薄膜的厚度较大时(如230nm),由晶格错配引起的应力通过位错的形式得以释放,YBCO薄膜的Tc变化不大.     

湿度对YBCO薄膜微观结构和超导性能的影响

文中采用无氟高分子辅助金属有机物沉积法( PA - MOD)在不同湿度条件下在LaAlO3单晶基底上制备了一系列YBCO超导薄膜.X射线衍射、扫描电镜和物性测量的结果表明,在成相热处理过程中气氛湿度对YBCO薄膜的结构和超导性能的有明显影响.干燥气氛成相的YBCO薄膜织构较好,表面较平整、致密,超导性能也较高,其临界超...     

铝、碳共掺提高MgB_2临界电流密度

本文研究了在MgBq超导体中Al,C及两种元素共同掺杂时对样品的超导转变温度,不可逆场和临界电流的影响.研究发现,少量的铝掺杂可以提高MgB2超导材料在低场下的临界电流密度,但由于对Tc的抑制而降低其在高场下的载流能力,而碳掺杂则可以有效提高MgB2超导材料的上临界场和不可逆场,从而达到改善其在高场下的载流能力的目的.研究发现,在0-7T外磁场范围内,1%铝和1%碳共同掺杂的样品表现出最佳的载流性能.钉扎力曲线的分析也应证了这一结果.     

Strongly enhanced flux pinning in the YBa_2Cu_3O_(7-X) films with the co-doping of Ba TiO_3 nanorod and Y_2O_3 nanoparticles at 65 K

YBa2Cu3O7-x(YBCO) films with co-doping BaTiO3(BTO) and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates(TFA-MOD). The properties of the BTO/Y2O3co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction(XRD), Raman spectra, and scanning electron microscope(SEM). The optimized content of yttrium excess in the BTO/Y2O3co-doped YBCO films is 10 mol.%, and the critical current density is as high as ~ 17 mA/cm2(self-field, 65 K) by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density(JC) not only at the self-magnetic field, but also in the applied magnetic field.     

Self-field reduces critical current density in thick YBCO layers

The engineering current density in YBCO coated conductor applications can be improved in two ways. Either the critical current density should be improved or the superconducting films made thicker. Unfortunately, it has often been observed that the average critical current density decreases when the thickness of films increases. Suggested reasons for this behaviour include e.g. two dimensional pinning properties, microcracks and imperfect crystallographic alignment. However, it is often forgotten that the self-field effect unavoidably reduces the critical current density when the thickness of YBCO films increases and thereby total current rises. In this paper, the influence of self-field on the average critical current density is studied computationally as a function of film thickness. The situation is also scrutinized at different external magnetic fields in order to find ways to distinguish self-field effects from problems related to the manufacturing process. For this purpose, critical current measurements in external field perpendicular to the film surface are proposed.     

一种新型YBCO高温超导带材临界电流特性测试方法

针对YBCO高温超导带材临界电流特性,文中基于四引线法,构造了一个集成有背景磁场发生装置的减压降温的低温测量装置。该装置包括一个提供背景磁场的双"E"形铁心线圈磁体;一个可以旋转0—360°的超导带材样本架以及一套可实现减压降温功能的低温测试系统。通过对低温杜瓦内温度、YBCO带材所处背景磁场大小、背景磁场与YBCO带材表面夹角的控制,实现了YBCO超导带材在不同温区、不同磁场及磁场方向下的临界电流特性的测量。这种新颖的测量方法和装置,综合考虑了环境温度、背景磁场和磁场方向变化的具体影响,能够获得较全面的YBCO高温超导带材临界电流性能参数。     

IBAD技术制备涂层导体用YSZ缓冲层长带的研究

在钇钡铜氧(YBCO)高温超导涂层导体制备路线中,离子束辅助沉积技术(IBAD)是两大主流技术路线之一,取得了最为突出的研究成果.本文简要介绍了IBAD技术制备YBCO涂层导体的最新研究进展;并采用离子束辅助沉积技术在哈氏合金(Hastelloy)基底上成功制备了1米长具有钇稳定氧化锆(YSZ)缓冲层的金属基带.采用X射线衍射仪(XRD)分析YSZ缓冲层的取向;利用原子力显微镜(AFM)和扫描电镜(FESEM)观察其表面形貌.获得了可以实际应用的IBAD-YSZ/Hastelloy缓冲层长基带,可以在该基带上研制其他缓冲层以制备YBCO高温超导涂层导体带材.     

The effect of BZO doping concentration and thickness dependent properties of YBCO films grown by PLD on buffered NiW substrates

The effect of BaZrO₃ (BZO) doping is systematically studied in YBa₂Cu₃O_6+x (YBCO) thin films deposited by pulsed laser deposition (PLD) on buffered NiW substrates. Based on the structural and magnetic properties, the optimal BZO doping concentration is obtained to vary between 4 and 7.5 wt.%, depending mainly on applied magnetic field. This relatively high optimal concentration is linked to the nanograined target material and metal substrate that cause low-angle grain-boundaries and in-plane spread of YBCO crystals on NiW. Thickness dependent analysis of undoped and BZO-doped YBCO films predicts differences in growth mechanisms where early growth next to the substrate interface is 2D-type in BZO-doped films. This leads to the situation where crystallographic structure as well as superconducting properties are improved when the film develops and the thickness is increased. Therefore from the resistivity measurements a threshold thicknesses where reasonable properties occur are determined for both set of films. Measurements in thermally activated flux-flow regime (TAFF) indicate that above the threshold thickness relatively strong and isotropic vortex pinning is realized in BZO-doped YBCO films. Generally, this paper demonstrates that especially for thin film applications on NiW substrates even more compatible buffer layer structures should be utilized.     

Enhanced flux pinning in pulsed laser deposited Y Ba2Cu3O7−δ : BaTiO3 nanocomposite thin films

The effect of incorporation of BaTiO₃(BTO) nanoparticles on the flux pinning properties of pulsed laser deposited YBCO:BTO thin films was studied. Substantial increase in the critical current density (J_C) and the pinning force density (F_p) of the nanocomposite thin films was observed. At 77 K, and zero applied magnetic field, the value of J_C for YBCO and YBCO:BTO (2%) thin films were 2.93 MA/cm² and 6.43 MA/cm², respectively. At the same temperature and an applied magnetic field of 4 T, the value of J_C increases from 3.6×10⁴ A/cm² for YBCO thin film to 2.7×10⁵ A/cm² for YBCO:BTO (2%) nanocomposite thin film. The study of temperature and field dependence of of YBCO and YBCO:BTO thin films indicates similar type of pinning. The lattice mismatch between YBCO and BTO seems to introduce more defects resulting in the improvement of flux pinning properties.     

Enhanced flux-pinning in fluorine-free MOD YBCO films by chemical doping

YBCO films without and with dilute cobalt and zinc doping were prepared on (0 0 l) LaAlO₃ substrate by non-fluorine metal organic deposition method. Effects of dilute cobalt and zinc doping on biaxial texture, microstructure and flux-pinning properties of YBCO films were investigated. The surface density and smoothness of the doped YBCO films have been distinctly improved compared with that of the pure film. Dilute cobalt- and zinc-doped YBCO films exhibit significantly enhanced J_c values in the magnetic field. The best result is achieved in the cobalt-doped YBCO film. At 77 K, J_c values of cobalt-doped film are 1.7 and 5.4 times higher than that of pure film in 0.5 T and 1.5 T, respectively. These results strongly suggest that dilute cobalt and zinc doping is a promising way to increase the current carrying capability of YBCO films.     

改进型前驱液对化学溶液法制备YBCO薄膜的影响

传统全三氟乙酸前驱液对涂敷环境湿度、低温预分解过程中的升温速率和水汽分压等因素具有敏感性,采用改进型前驱液可以降低其敏感性,从而有利于涂层导体的连续制备.我们提出的改进型前驱液中,三氟乙酸钇、三氟乙酸钡和苯甲酸铜是前驱体,甲醇和丙酸的为溶剂.采用化学溶液法在铝酸镧单晶衬底上制备YBCO,低温分解阶段以1～5℃/min快速升温,可以获得低温后的前驱膜光滑完整,无裂纹.通过X衍射分析和扫描电镜分析了薄膜的织构和表面微结构,四引线法测试薄膜超导电性.采用改进型前驱液制备的薄膜超导转变温度(Tc)为90K,在77K、自场下临界电流密度(Jc)为1MA/cm2.     

前驱液成分对TFA-MOD法制备YBa2Cu3O7-x薄膜超导性能的影响

采用三氟乙酸盐-金属有机沉积法(TFA-MOD)在铝酸镧单晶基体上制备了YBa₂Cu₃O_7-x (YBCO)超导薄膜.通过改变前驱液的成分,研究了金属元素的不同化学计量比对YBCO薄膜的结构和性能的影响.结果表明,按照钇盐Y(CH₃COO)₃与钡盐Ba(CH₃COO)₂的比例为Y ∶Ba=1 ∶1.5时所制备的YBCO薄膜的临界电流密度比严 关键词： 三氟乙酸盐-金属有机沉积 钇钡铜氧薄膜 前驱液成分 磁通钉扎     

Activation energy in La0.7Ca0.3MnO3/YBa2Cu3O7-δ / La0.7Ca0.3MnO3 superconducting trilayers

Resistivity vs. temperature measurements on La_0.7Ca_0.3MnO₃/YBa₂Cu₃O_7-δ /La_0.7Ca_0.3MnO₃ (LCMO/YBCO/LCMO) trilayers with different YBCO thickness, were performed in external magnetic field H up to 8 T. By evaluating the activation energy U from the slope of the resistivity Arrhenius plot, a strong depression of U has been observed when decreasing the YBCO layer thickness and the absolute U values appear to be reduced with respect to the values reported in literature in the case of YBCO thin films and YBCO/insulating multilayers. Moreover, a logarithmic U vs. H dependence is shown both in the case of thick and thin YBCO layers indicating the formation of a two dimensional vortex lattice. The experimental data are discussed considering the strong influence of the ferromagnetic LCMO on the superconducting YBCO properties which reduces the effective YBCO thickness more than predicted by the conventional theories.