Nb5+掺杂对低氟MOD法制备的YBCO薄膜性能的影响

本研究通过低氟MOD法成功地制备了Nb⁵⁺掺杂的YBa₂Cu₃O_7-x(YBCO)薄膜, Nb⁵⁺在薄膜中生成了大小在20~30 nm之间的纳米颗粒; 纳米颗粒的生成不会对 YBCO薄膜的织构和临界温度(T_c)构成明显的影响。由于纳米颗粒的引入, 掺杂后薄膜的临界电流密度(J_c)在整个磁场范围内都要高于纯的YBCO, 自场下的Jc更是达到了3.4 MA/cm²。掺杂薄膜的钉扎力(F_p)也远远大于纯YBCO, 最大钉扎力达到了3.25 GN/m³, 有效地提高了YBCO在外加磁下的超导性能。     

正负错配纳米颗粒掺杂对YBCO薄膜性能影响的研究

利用低氟MOD工艺制备了Ba₂YTaO₆(BYTO)单一纳米颗粒掺杂及BYTO和LaAlO₃(LAO)双纳米颗粒共掺杂的YBCO复合薄膜。研究表明BYTO在YBCO薄膜中的最优掺杂量为6mol%, 此时薄膜的自场J_c为1.25 MA/cm ², 在1.2 T下获得的最大钉扎力为3.02 GN/m ³。共掺杂试验中引入与YBCO具有正错配度的BYTO粒子和负错配度的LAO粒子, 两者相互作用使有效掺杂总量提高至10mol%。调整两种纳米粒子的配比发现6mol% BYTO+4mol% LAO掺杂的YBCO复合薄膜样品在外加磁场为2 T时, J_c值高达0.27 MA/cm ², 获得最大钉扎力时的磁场由纯YBCO薄膜的0.42 T提高至共掺杂的1.6 T, 此时最大钉扎力为5.6 GN/m ³。正负错配纳米颗粒共掺杂有效地提高了YBCO复合薄膜在外加磁场下的超导性能。     

MOD方法制备Y0.5Yb0.5BCO薄膜及其性能研究

采用低氟金属有机物沉积工艺, 通过将浓度相同的YBCO、YbBCO前驱溶液按1: 1的体积比混合, 使元素Yb部分取代Y, 成功制备了Y_0.5Yb_0.5BCO薄膜. 该薄膜成份单一, 具有很好的双轴织构; 薄膜表面平整致密, 没有裂纹和孔洞, 元素分布均匀. 虽然Yb部分取代Y降低了薄膜的临界转变温度(T_c), 但有效提高了薄膜在高场下的场性能, 如在77K, 3T磁场下, Y_0.5Yb_0.5BCO薄膜的J_c值提高了1.26倍. 为了进一步改善薄膜在低场下的性能, 通过在Y_0.5Yb_0.5BCO前驱溶液中再加入6 mol%的TaCl₅, 成功地制备了Ta⁵⁺掺杂的Y_0.5Yb_0.5BCO薄膜, 提高了薄膜在整个磁场范围内的载流能力.     

低氟MOD法制备Zr掺杂YBCO薄膜的研究

在金属有机盐沉积（MOD）法制备YBCO薄膜的工艺中, 采用无F的α甲基丙烯酸铜取代原来的三氟乙酸铜, 可以降低前驱溶液中大约50%的氟含量. 研究表明, 该方法大大缩短了YBCO前驱薄膜受热分解的时间, 仅为原来的1/7. 通过XRD、SEM分析发现, 该方法可以制备成分单一、具有良好立方织构的YBCO薄膜, 且薄膜表面平整致密, 没有裂纹, 临界温度(T_c)达到了90K左右, 77K、自场下的临街电流密度(J_c)达到了2.84MA/cm². 通过在制备的YBCO薄膜中引入6mol% 的 Zr元素掺杂, 有效地提高了YBCO薄膜在外加磁场下的超导性能.     

YBa2Cu3O7-δ薄膜的BaCl2/BaF2-MOD法制备及超导特性研究

传统三氟乙酸金属有机化学溶液沉积法(TFA-MOD)制备YBa₂Cu₃O_7-δ (YBCO)超导层,Ba倾向于与F结合,从而避免BaCO₃的形成。本工作开展了新型基于BaCl₂/BaF₂途径的化学溶液法生长YBCO超导薄膜的研究。重点研究了添加Cl对YBCO薄膜晶粒取向、微观结构和超导性能的影响,并通过生长反应的热化学计算,分析了BaCl₂途径YBCO薄膜的物相转变机制。结果表明:添加Cl有利于抑制a轴晶粒取向,促进c轴晶粒成核。添加Cl的YBCO双层膜起始转变温度(Tc-onset)没有明显变化,约为89.6 K,其临界电流密度(Jc)显著提升, Jc达到2.07 MA/cm²(77K,自场)。此外,生长反应过程的物相转变分析表明Cl优先与Ba结合形成BaCl₂,有效避免BaCO₃的形成。本研究结果表明:添加Cl对制备YBCO超导厚膜有促进作用,这为MOD法制备YBC...     

高性能Y_(0.5)Gd_(0.5)BCO薄膜的研究

通过在YBCO前驱溶液中加入醋酸钆(Gd(CH_3COO)_3),使元素Gd部分取代Y,成功地制备了Y_(0.5)Gd_(0.5)BCO薄膜,该薄膜成分单一且具有很好的c轴取向.通过对Y_(0.5)Gd_(0.5)BCO薄膜和YBCO、GdBCO薄膜的超导性能比较发现,虽然Y_(0.5)Gd_(0.5)BCO薄膜的临界转变温度(T_c)(约为90.5 K)较YBCO和GdBCO薄膜有所下降,但是在65K、自场下,Y_(0.5)Gd_(0.5)BCO薄膜具有最高的临界电流密度(J_c)值,为4.87MA/cm~2.且随着外加磁场的增加,J_c值提高的较多.在3T的磁场下,Y_(0.5)Gd_(0.5)BCO薄膜的J_c值分别是纯GdBCO和YBCO薄膜的1.8倍和5.1倍.此外,替代还有效提高了薄膜的磁通钉扎力.     

Nb掺杂YBCO薄膜钉扎机理的研究

通过低氟MOD法制备了Nb掺杂的YBa₂Cu₃O_7-x(YBCO)薄膜, 掺入的Nb以Ba₂YNbO₆(BYNO)相存在, 其尺寸大小在20~30 nm之间, 薄膜中BYNO纳米颗粒以外延和随机两种取向共存, 且以随机取向为主。BYNO纳米颗粒的周围出现堆垛层错, 并且BYNO周围的YBCO出现严重的晶格畸变, 这增加了YBCO薄膜内部的微观应变, 且随机BYNO颗粒含量越高, YBCO薄膜内部的微观应变就越大。微观应变增加了薄膜的磁通钉扎能力, 进而提高了薄膜在高磁场下的超导性能。     

Gd掺杂对PZT薄膜介电性能及极化行为的影响

采用sol-gel法在Pt/Ti/SiO₂/Si衬底上制备出高度(100)择优取向的Gd掺杂PZT薄膜(简写为PGZT); 介电测试结果表明, 1mol%Gd掺杂的PZT薄膜介电常数最大, 2mol%Gd掺杂PZT薄膜与未掺杂薄膜的介电常数相差不大, Gd掺入量>2mol%时, 薄膜的介电常数下降; 薄膜的不可逆极化值呈现与介电常数相同的变化趋势, 而可逆极化值变化较小. 在弱电场下(低于矫顽场E_c), 用瑞利定律分析薄膜介电常数随电场强度的变化规律, 1mol%Gd掺杂的薄膜瑞利系数α最大, 说明薄膜中缺陷的浓度最低. 1mol%Gd掺杂的薄膜介电和铁电性能的改善与Gd³⁺在PZT晶格中的占位情况有关.     

Ba源配比对MOCVD法制备YBCO薄膜性能的影响研究

采用单一液相混合源进液及闪蒸的MOCVD系统在LaAlO₃(001)单晶基片上制备YBa₂Cu₃O_7-x(YBCO)薄膜, 研究混合源中Ba含量对YBCO超导薄膜成分、结构及电流承载能力的影响。结果表明, 当Ba含量较小时, YBCO薄膜中易于形成尺寸较小的CuO颗粒; 随着Ba含量的增加, 薄膜中形成Ba₂CuO₃晶粒, 并且Ba₂CuO₃晶粒尺寸随Ba含量的增加而逐渐增大。杂质相的含量、尺寸以及与YBCO的晶格匹配程度对YBCO薄膜的双轴取向生长和电流承载能力具有重要影响。当原料摩尔配比Ba/Y=3.9时, 成功制备出了具有优异面内面外取向、结构致密的YBCO超导薄膜, 77 K下的300 nm厚度薄膜的临界电流密度达到4.0 MA/cm², 该研究结果对于第二代涂层导体的发展具有重要意义。     

氧化锆掺杂铝硅复合气凝胶耐热性能研究

采用正丁醇锆作为锆源,通过溶胶凝胶法以及超临界乙醇干燥制备氧化锆气凝胶,并使用仲丁醇铝以及二甲基二乙氧基硅烷对其掺杂制备Zr-Al以及Zr-Si复合气凝胶,利用FESEM、XRD、FT-IR以及比表面积和孔结构分析仪对气凝胶形貌、尺寸和结构进行表征。结果表明复合铝后的气凝胶密度从0.393 g/cm³降低到0.147 g/cm³,复合硅后的气凝胶比表面积从178 m²/g上升到394 m²/g,耐温性能也显著提高,FESEM照片显示,热处理后Al与Si掺杂的气凝胶形貌变化较小,Zr-Si复合气凝胶在900℃热处理4h之后比表面积仍为168 m²/g,并没有出现ZrO₂的相变。氧化锆气凝胶掺杂铝及硅元素之后,有效抑制氧化锆的相变从而提高其耐温性能。     

超声雾化方法中两步沉积对YBCO薄膜性能的影响

用自行研制的超声雾化装置在{110}<011>织构的Ag基带上直接沉积了YBCO涂层超导薄膜, 结果发现一步沉积所得YBCO薄膜的表面有许多白色小颗粒, 而且薄膜的织构和临界电流密度都较低, 这是在900℃高温沉积过程中大量的Ag蒸发和扩散到YBCO膜层中所致. 于是本文提出分高低温两步沉积的实验方案, 即700℃先沉积15min, 再升温到900℃沉积30min, 通过SEM对薄膜表面和EDS能谱对薄膜的断面进行分析可知, 两步沉积的YBCO薄膜中Ag的含量大大降低, 而且薄膜的织构和临界电流密度得到明显改善和提高, 最后通过两步沉积制备了15cm长、临界电流密度高于10⁴A/cm²的YBCO超导薄膜.     

Zn^2＋掺杂的YBCO薄膜的超导性能研究

采用溶胶-凝胶法在LaAlO3（LAO）单晶衬底上制备了Zn^2＋掺杂的YBCO薄膜,用X射线衍射（XRD）、高分辨透射电子显微镜（HRTEM）以及标准四引线法分别研究了Zn^2＋掺杂的YBCO薄膜的微观结构、生长取向以及超导性能。结果表明,随Zn2＋掺杂浓度的增大薄膜的临界电流密度提高,而临界转变温度下降、临界转变温区变宽;但当掺杂量〉0.5%（摩尔分数）时,会影响YBCO的c轴取向生长,导致超导性能变差。通过优化掺杂比例后得到Zn2＋掺杂0.5%（摩尔分数）的YBCO薄膜具有最好的综合超导性能,其TC为91.3K,ΔT为1.1K,Jc约为1.54MA/cm^2（77K,0T）。     

大面积YBCO高温超导双面薄膜的生长研究

采用倒筒式直流溅射(ICS)方法,辐射方式加热基片,通过电机带动基片旋转,在两面同时溅射沉积YBCO高温超导双面薄膜。在加热温度为850℃,总压强为35Pa,氧氩比为1∶2,靶基距50mm,基片转速5～40r／min条件下,在20mm×20mm的LaAlO     

Y2BaCuO5粒子在准单畴Y-Ba-Cu-O超导块材中的分布及其对超导性能的影响

采用顶部籽晶熔融织构法制备了Y-Ba-Cu-O(YBCO)准单畴超导块材,研究了Y2BaCuO5(Y211)粒子在块材中的分布及其对临界电流密度(Jc)和磁悬浮力性能的影响.扫描电子显微镜(SEM)观察发现,Y211颗粒在准单畴超导块材中的分布是不均匀的.实验结果表明,Y211平均粒径的大小与样品的磁悬浮力和临界电流密度成反比,Y211相粒子在母体中的分布越均匀,粒子平均粒径越小,越有利于提高临界电流密度和磁悬浮力.对于φ20mm的YBCO单畴块材,磁悬浮力可以达到33N(77K,0.55T),临界电流密度达到6.6×104 A/cm2.     

Comparison of Flux Pinning Mechanism in Laser Ablated YBCO and YBCO:BaZrO3 Nanocomposite Thin Films

Thin films of YBCO and YBCO:BaZrO₃ (BZO) nanocomposite have been deposited using the pulsed laser deposition technique. Substantial increase in critical current density (J _C ) and pinning force density (F _p ) of the nanocomposite thin films was observed. The possible pinning mechanism in YBCO:BZO nanocomposite thin films has been explored and compared with the pinning mechanism in pure YBCO thin film by studying the variation of J _C with magnetic field (B) and temperature. In the intermediate field regime (0.1–1 T), J _C follows B ^−α with nearly similar values of α for YBCO and YBCO:BZO nanocomposite thin films indicating similar pinning mechanism in both thin films. The variation of J _C with reduced temperature (t=T/T _C ) has been studied for both the films and it was observed that the mechanism of pinning in both YBCO and YBCO:BZO thin films is similar (δT _C pinning). The observed enhanced values of J _C and F _p of the nanocomposite thin film is attributed to the presence of BZO nanoparticles, which induces more defects due to lattice mismatch between YBCO and BZO leading to improved flux pinning properties of the nanocomposite thin film.     

Reel-to-Reel PLD Fabrication of YBCO Coated Conductor by Single and Multi-coating Processes

YBa₂Cu₃O_7?δ (YBCO) coated conductors have been fabricated on CeO₂/YSZ/Y₂O₃ buffered Ni-5at%W tapes by pulsed laser deposition (PLD) using the reel-to-reel process. A multi-coating process for YBCO film was employed, and single and multi-coating methods for YBCO films are compared. X-ray diffraction texture measurements showed good in-plane and out-of-plane crystalline orientations for the YBCO films. Magnetic measurements were carried out on the samples, and the critical current density as a function of the magnetic field was investigated. The results showed that the superconducting properties of YBCO films fabricated by the multi-coating process were better than those prepared by the single coating process.     

Fabrication and Analysis of Tri-layer YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Thick Films by Low-Fluorine MOD Method

Improving the thickness of superconducting layer in coated conductors is an effective way to enhance its critical current. In this work, tri-layer YBCO/YBCO/YDyBCO films were successfully deposited on buffered Hastelloy substrate using the multi-coating lowfluorine metal-organic decomposition (LF-MOD) method and the thickness of the films can be up to 2.4 μ m. The effects of high-temperature annealing time on microstructures and superconducting properties of the films were systematically studied. Energy dispersive X-ray spectroscopy (EDS) results reveal that there remains a large amount of F element in the upper layer of the film when the annealing time is too short. With increasing the annealing time, the fluoride-containing precursor converts to YBCO grains completely. But the coarsening of grains appeared, and the critical current density (J _c) of the film dropped slightly when the annealing time is too long. The cross-sectional scanning electron microscope (SEM) image and EDS plane analysis were applied to investigate the microstructure and element distribution of the final triple-layer YBCO films, respectively. The critical current of the final YBCO superconducting film could reach 316 A (77 k, self-field) for 1.2-cm-wide tapes with the optimal annealing conditions.     

Dependence of Microstructure and <Emphasis Type="Italic">J</Emphasis><Subscript>c</Subscript> of YBCO Films on CeO<Subscript>2</Subscript> Cap Layers Deposited by Multi-plume PLD

In order to achieve high-performance YBa₂Cu₃O_7?x (YBCO)coated conductors (CCs) fabricated in industrial scale, it is necessary to enhance the transport properties and production speed of the CCs for use in various application forms. The transport performance of CCs depends upon the inner structure of the conductors, which make it important to analyze the microstructure and transport properties. The thickness of the buffer layer is a factor in improving speed. In this work, we deposited YBCO films on CeO₂ cap layers with different thicknesses ranging from 21 to 563 nm by multi-plume pulsed laser deposition (PLD) and investigated the dependence of the microstructure and superconducting properties of YBCO film on the thickness of CeO₂ films. The crystalline structure and surface morphology of YBCO films are systematically characterized by means of XRD, AFM, SEM and TEM. The critical current of YBCO film was measured by the conventional four-probe method at 77 K, in self-field. The results showed that the microstructure and superconducting performance of YBCO film were strongly dependent on the thickness of CeO₂ films. At the optimal CeO₂ layer thickness of 221 nm, the YBCO film exhibited a sharp in-plane and out-of-plane texture of full width at half maximum (FWHM) values of 1.5° and 2.4°, respectively, and smooth morphology of root mean square (RMS) value as low as 4.0 nm. The sharply biaxially textured YBCO films with the critical current density as high as 4.7 × 10⁶ A/cm² (77 K, in self-field) were obtained on CeO₂/MgO/Y₂O₃/Al₂O₃/C276 architecture.