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     

纳米微粒BaFe12O19掺杂对单畴超导块材GdBa2Cu3O7-δ性能的影响

磁通钉扎性能对GdBa₂Cu₃O_7-δ超导块材的实际应用具有重要的影响, 而引入合适的第二相粒子可以改善GdBa₂Cu₃O_7-δ 超导块材的磁通钉扎性能.本文采用顶部籽晶熔融织构法成功地制备出纳米微粒BaFe₁₂O₁₉(<100 nm)掺杂的超导块材, 样品的最终组分为Gd123+ 0.4 Gd211+ x BaFe₁₂O₁₉ (x=0, 0.2 mol%, 0.4 mol%, 0.8 mol%)+ 10 wt%Ag₂O+ 0.5 wt%Pt. 通过研究不同掺杂量的BaFe₁₂O₁₉微粒对GdBa₂Cu₃O_7-δ 超导块材微观结构和超导性能的影响, 结果表明当掺杂量为0.2 mol%时, 样品的临界电流密度几乎在整个外加磁场下都有明显的提高.在零场下, 临界电流密度达到5.5× 10⁴ A/cm². 纳米微粒BaFe₁₂O₁₉不仅可以保持掺杂前的化学组成, 作为有效的钉扎中心存在于超导块材中, 并且能够改善Gd₂BaCuO₅粒子的分布和细化Gd₂BaCuO₅粒子, 使Gd₂BaCuO₅粒子的平均粒径由未掺杂时的1.4 μ m减小到掺杂后的0.79 μ m, 进而提高了超导块材的临界电流密度和俘获磁场, 明显提高了GdBa₂Cu₃O_7-δ 超导块材的超导性能.临界温度T_C也有所提升, 并能够维持在92.5 K左右. 该结果为进一步研究纳米磁通钉扎中心的引入并改善GdBa₂Cu₃O_7-δ 超导块材的性能有着重要的意义.     

插入二氧化铈薄膜提高MOD-YBa2Cu3O7-x厚膜超导性能的研究

YBa₂Cu₃O_7-x(YBCO)膜存在“厚度效应”: 随着厚度增加, YBCO薄膜的临界电流密度下降, 尤其是YBCO薄膜的厚度超过1 μm时, 它的临界电流密度急剧下降. 本文在YBCO薄膜之间引入极薄的二氧化铈(CeO₂)薄膜, 成功制备出结构为YBCO/YBCO/CeO₂/YBCO的超导厚膜. 所制备的厚度为2 μm的YBCO膜临界电流密度为1.36 MA/cm² (77 K, 自场), 其性能比相同厚度的纯YBCO膜有了较大幅度的提升. 研究表明CeO₂薄膜起到了传递织构、松弛应力的作用.     

NdBa2Cu3O7-δ/YBa2Cu3O7-δ多层膜体系的外延结构和磁通钉扎的研究

采用脉冲激光沉积技术,在单晶SrTiO₃基底上外延生长了一系列名义结构为p×(NdBa₂Cu₃O_7-δ(m)/YBa₂Cu₃O_7-δ(n))的多层膜和准多层膜(单元层NdBa₂Cu₃O_7-δ较厚而YBa₂Cu₃O_7-δ呈非连贯的岛状分布,m,n为激光脉冲数,p为重复周期).样品的超导转变温度在87—91 K范围,具体大小取决于不同的调制结构,多层膜的重复周期越大,层状界面越多,超导转变温度就越低.磁传输测量表明,准多层的样品不仅具有较高的超导转变温度,而且具有较强的磁通钉扎性能,77K零场下的临界电流密度高达4×10⁶ A/cm²,显示出良好的应用前景. 关键词： 2Cu₃O_7-δ')" href="#">NdBa₂Cu₃O_7-δ 多层膜 磁通钉扎 临界电流密度     

高温超导YBa2Cu3O7-δ-Y2O3多层薄膜的制备及性能表征

采用脉冲激光沉积技术(PLD)在LaAlO3(100)单晶衬底上外延生长YBa2Cu3O7-δ-Y2O3多层薄膜,用X射线衍射技术(XRD)分析薄膜的物相结构和外延特性,通过原子力显微镜(AFM)观察薄膜的表面形貌.本文主要研究了最佳工艺参数下交替生长多层YBCO-Y2O3膜的超导性能.结果表明,YBa2Cu3O7-δ-Y2O3薄膜为纯c轴取向外延生长,临界电流密度Jc(H=0或H//C)均高于纯YBCO薄膜,纳米Y2O3起到磁通钉扎中心作用.     

Y2O3:Eu纳米晶中能量传递相互作用的研究

通过浓度猝灭曲线确定了引起Y₂O₃纳米晶中Eu³⁺发光浓度猝灭的是交换相互作用.测量了两种颗粒尺寸下Eu³⁺的⁵D₀—⁷F₂跃迁发光衰减曲线随掺杂浓度的变化,利用交换相互作用的理论衰减曲线对实验衰减曲线进行拟合.计算Eu³⁺离子的交换相互作用能量传递的效率,分析了Y₂O_{3关键词： 能量传递 2}O₃Eu纳米晶')" href="#">Y₂O₃Eu纳米晶 发光衰减     

尺寸效应对Er3+掺杂纳米Y2O3的发光特性的影响

采用燃烧法制备了不同尺寸的Er³⁺掺杂Y₂O₃粉体材料,研究了尺寸效应对Er³⁺掺杂纳米Y₂O₃材料发光特性的影响.光声光谱显示,对于不同晶粒尺寸的样品,Er³⁺离子光声峰位置几乎保持不变.这表明小尺寸效应对稀土离子能级位置影响很小.对488nm激光激发下的发射谱的分析发现,随着样品颗粒尺寸的减小,4S_3/2能级和关键词： 3+离子')" href="#">Er³⁺离子 纳米 发光 能量传递     

YZr2OZr3:Er3+纳米晶anti-Stokes发光性质的研究

采用均相沉积法制备了不同Er³⁺离子浓度掺杂的Y₂O₃纳米晶, 应用XRD，SEM和PL光谱对该体系材料进行了表征.在Y₂O₃:Er³⁺纳米材料体系中, 观察和研究了Stokes及anti-Stokes PL谱强度与Er³⁺离子摩尔浓度变化的关系, 当Er³⁺离子浓度为2.0mol%时, anti-Stokes PL强度最强.粉末X 关键词： 氧化钇纳米晶 anti-Stokes PL 双光子吸收     

金属有机溶剂法Y1Ba2Cu3O7-δ超导薄膜的Ce掺杂效应

通过三氟乙酸盐-金属有机物沉积方法（TFA-MOD）研究了Ce掺杂对钇钡铜氧（YBCO）超导薄膜性能的影响.观察到10 mol%Ce掺杂使YBCO超导薄膜的c轴取相降低,出现明显的a轴晶粒,薄膜表面变得粗糙.尽管超导临界温度稍有减小,其超导临界电流密度（Jc）在高磁场下性能获得了有效提高,当外磁场强度达到2T时,超导薄...     

YBa2Cu3O7-δ外延薄膜的有效钉扎势

在0—7T磁场范围内，测量了不同测量电流密度下YBa₂Cu₃O_7-δ外延薄膜的电阻温度关系.实验结果表明，临界温度以下，混合态的耗散电阻率能很好地用热激活磁通蠕动描述.有效钉扎势的电流密度关系遵守Zeldov等人提出的对数关系，有效钉扎势的温度和磁场关系遵守U∝(1-T/T_c)H^-α关系，其中α=0.63，与热激活磁通点阵位错运动模型相一致，表明样品具有2D涡旋性质. 关键词：     

Strong flux pinning enhancement in YBa2Cu3O7-x films by embedded BaZrO3 and BaTiO3 nanoparticles

YBa2Cu3O7-x (YBCO) films with embedded BaZrO3 and BaTiO3 nanoparticles were fabricated by metalorganic deposition using trifluoroacetates (TFA-MOD). Both X-ray diffraction and transmission electron microscopy revealed that these BaZrO3 and BaTiO3 nanoparticles had random orientations and were distributed stochastically in the YBCO matrix. The unique combined microstructure enhances the critical current density (Jc) of the BaZrO3/BaTiO3 doped-YBCO films, while keeping the critical transition temperature (Tc) close to that in the pure YBCO films. These results indicate that BaZrO3 and BaTiO3 nanoparticles provide strong flux pinning in YBCO films.     

低能离子对高温超导YBa_2Cu_3O_(7-δ)薄膜的表面改性和机理

低能氩离子束轰击并后退火处理的离子束表面改性,会影响高温超导薄膜的表面结构和超导特性,但是其中的深刻微观机理不清楚.本文通过连续改变离子束轰击时间,系统研究了离子束表面改性对于超导膜结构和临界电流密度的影响.通过扫描电子显微镜、X射线衍射、J_(c-scanning)测试表征样品的结构特性和超导特性,并得出内应变、氧空位缺陷等参量.研究表明,经过表面改性的钇钡铜氧(YBa_2Cu_3O_(7-δ),YBCO)薄膜,随轰击时间增加表面形貌会变得更加均匀致密,a轴晶粒消失,并且临界电流密度有了显著的提高.由化学键收缩配对模型分析得出,临界电流密度的提高与薄膜内应变增大和引发的局部YBCO结构中Cu—O键收缩有关.     

The weak center nature and their pinning anisotropy of radiation damage defects in Y1Ba2Cu3O7−δ single crystals

A field induced weak pinning center, in MeV proton irradiated Y₁Ba₂Cu₃O_7−δ (YBCO) single crystal and in ⁶Li-doped sintered YBCO exposed to thermal neutron irradiation, has been identified. The pinning contribution of those radiation caused weak centers (RWCs) showed strong field dependence, which resembles that of the common weak centers of oxygen deficient regions (OWCs) in most of the bulk YBCO materials. The radiation dose dependence of the pinning enhancement, in proton irradiated single crystal, showed strong angular dependence, when the field orientation relative to the crystal was changed. This is believed to be due to the different flux line size (orξ) in different directions, and the so caused volume or line pinning effects. No angular dependence has been observed in neutron irradiated YBCO, which is polycrystalline in nature.     

Ni2O3掺杂对新固相源顶部籽晶熔渗生长法制备单畴GdBCO超导块材超导性能的影响

本文通过在新固相源中添加Ni₂O₃的方法, 采用顶部籽晶熔渗生长工艺(TSIG)制备出组分为(1-x) (Gd₂O₃+1.2BaCuO₂)+x Ni₂O₃、直径为20 mm的单畴GdBCO 超导块材(其中x = 0, 0.02, 0.06, 0.10, 0.14, 0.18, 0.30, 0.50 wt%), 并研究了Ni₂O₃的掺杂量x对样品的表面生长形貌、微观结构、临界温度T_c、磁悬浮力以及俘获磁通密度的影响. 研究结果表明, 当Ni₂O₃的掺杂量x在0–0.50 wt%的范围内时, 均可制备出单畴性良好的样品, 且Ni₂O₃的掺杂对样品中Gd211粒子的分布和粒径没有明显的影响. 在Ni₂O₃的掺杂量x从0增加到0.50 wt%的过程中, 样品的临界温度T_c呈现下降的趋势, 从x=0时的92.5 K下降到x=0.50 wt%时的86.5 K, 这是由于Ni^{3 +}替代GdBCO晶体中Cu^{2 +}所致; 样品磁悬浮力和俘获磁通密度均呈现先增大后减小的变化规律, x=0.14 wt%时, 磁悬浮力达到最大值34.2 N, x=0.10 wt%时, 俘获磁通密度达到最大值0.354 T. 样品磁悬浮力和俘获磁通密度的变化规律与Ni₂O₃的掺杂量x有密切关系, 只有当掺杂量x合适时, Ni³⁺对Cu^{2 +}的替代既不会造成T_c的明显下降, 但又能产生适量的Ni^{3 +}/Cu²⁺ 晶格畸变, 从而达到提高样品磁通钉扎能力和超导性能的效果.     

High critical current density YBa2Cu3O7−δ tapes prepared by the surface-oxidation epitaxy method

YBa₂Cu₃O_7−δ (YBCO) films with high critical current density (J_c) were successfully fabricated on nickel tapes buffered with epitaxial NiO. NiO was prepared on the textured nickel tape by the surface-oxidation epitaxy (SOE) method. We have reported so far a critical temperature (T_c) of 87 K and J_c=4–6×10⁴ A/cm² (77 K, 0 T) for the YBCO films on NiO/Ni tapes. To enhance the superconducting properties of the YBCO films on the SOE-grown NiO, depositions of thin oxide cap layers such as YSZ, CeO₂, and MgO on NiO were investigated. These oxide cap layers were epitaxially grown on NiO and provided the template for the epitaxial growth of YBCO films. Substantially improved data of T_c=88 K and J_c=3×10⁵ A/cm² (77 K, 0 T) and 1×10⁴ A/cm² (77 K, Hc, 4 T) were obtained for YBCO film on NiO, by using a MgO cap layer with a thickness of 50 nm. The method described in this paper is a simple way to produce long YBCO tape conductors with high-J_c values.     

Evidence for pinning by (Sr,Ca)2CuOy particles in partial-melting processed bulk Bi2Sr2CaCu2O8+δ ceramics

Flux distributions of partial-melting processed Bi₂Sr₂CaCu₂O_8+δ ceramics are obtained using magneto-optic imaging. In remanent states (μ₀H_a=0 T), large amounts of trapped flux are observed along (Sr,Ca)₂CuO_y particles embedded in the Bi₂Sr₂CaCu₂O_8+δ matrix. Despite the relatively large size of these particles (up to 30 μm), the pinning effect is similar to that of Y₂BaCuO₅ particles in melt-processed YBa₂Cu₃O_7−δ. Furthermore, we discuss how the pinning capability of non-superconducting particles of different sizes and densities will show up in magneto-optic images.     

Vortex pinning in polycrystalline Eu1.5Ce0.5Sr2Cu2NbO10 from rotational magnetic measurements

Rotational magnetization-vector measurements were carried out on a superconducting polycrystalline disk of EuCSCNO. The results at 4.2 K and low fields resemble recent results for YBa₂Cu₃O_7−δ (YBCO) and Ba_0.57K_0.43BiO₃ (BKBO) in revealing a broad distribution in the strength of the vortex pinning torques. This resemblance extends to higher fields, where it was found that the average pinning torque per vortex (τ_p), which is directly related to the critical current density, decreases steadily with increasing field in a manner consistent with vortex bundling. Quantitatively, however, the values of τ_p for EuCSCNO are smaller by an order of magnitude than those for YBCO but are only moderately smaller than those for BKBO. This comparison supports the notion that the vortex pinning may derive in part from deviations from oxygen stoichiometry, which are normally present in YBCO but are essentially absent in EuCSCNO and BKBO. Moreover, as in YBCO and BKBO, the τ_p in EuCSCNO at fixed field is found to diminish rapidly as the temperature rises towards T_c.     

Ba1-xKxFe2As2单晶(Tc=38.5K)磁通钉扎力与钉扎机理研究

铁基超导体是在2008年由Hosono发现的一种新型超导材料, 由于其具有上临界场高、各向异性小、临界电流密度大等优点, 在世界范围内引起了广泛关注. 以Ba_1-xK_xFe₂As₂为代表的FeAs-122系超导体具有结构简单、合成温度低、单晶容易制备等优点, 是物理学家和材料学家关注的焦点. 本工作在获得最优化掺杂的Ba_1-xK_xFe₂As₂单晶(T_c = 38.5 K)基础上, 通过分析其在不同磁场条件下电阻温度变化关系、不同温度条件下的磁滞回线等数据, 系统的研究了Ba_1-xK_xFe₂As₂单晶磁通钉扎力和磁通钉扎机理. 研究发现Ba_1-xK_xFe₂As₂超导体具有非常高的磁通钉扎势, 其中9 T的外场条件下, 其在H//c轴和H//ab面的钉扎势分别为5800 K和8100 K, 展示出良好的应用前景; 通过进一步分析发现, 其磁通钉扎机理应是由于晶格内部的小尺寸缺陷引起的电子平均自由程变化而导致的δl钉扎.     

Flux jump avalanches in torque studies of single crystal YBa2Cu3O7−δ

A series of avalanche-like jumps are observed in the mixed state of single crystal YBa₂Cu₃O_7−δ (YBCO) superconductors. Emerging as a saw-tooth pattern in torque vs. sample orientation in magnetic field, these jumps are discontinuous on our most resolute angular scale. While reminiscent of the classical flux jump instability, the present jumps are instead proposed to be associated with the layered nature of the material and twin boundary (TB) pinning, the combination of which promotes a crossover from a tilted to a kinked vortex structure.