多层膜外退火方法制备MgB2超导薄膜

报道了利用电子束蒸发的Mg/B多层膜作为前驱体，然后退火制备MgB₂薄膜的工作. 实验中发现，采用翻转膜面的退火处理方式可以有效地避免降温过程中Mg蒸气在薄膜表面形成的颗粒凝结，由此稳定地实现了面积为10 mm×10 mm，均匀、平整的超导薄膜的制备，T_c达35 K，转变宽度为0.8 K，在5 μm×5 μm的区域内薄膜的平均粗糙度小于10 nm. 为了便于后续器件制作过程中的微加工工艺，研究了膜厚小于1000 ?时薄膜的成相规律，发现当样品厚度减薄后，T_c会有明显降低. 通过调整前驱薄膜中的不同分层厚度，仍可实现转变温度达30 K以上、厚度约600 ?的MgB₂薄膜，在20 K时的临界电流密度为2.4×10⁶ A/cm².     

钛离子辐照对MgB2超导薄膜的载流能力和磁通钉扎能力的影响

利用混合物理化学气相沉积法(hybrid physical-chemical vapor deposition, HPCVD)可以制备出高性能的MgB₂超导薄膜, 再对薄膜进行钛(Ti)离子辐照处理.经过辐照处理后的样品被掺入了Ti元素, 与未处理的干净MgB₂样品相比,其超导转变温度没有出现大幅度的下降, 而在外加磁场下的临界电流密度得到了明显的提高,同时样品的上临界磁场也得到了提高. 在温度5 K, 外加垂直磁场为4 T的情况下, Ti离子辐照剂量为1× 10¹³/cm²的样品的临界电流密度达到了1.72× 10⁵ A/cm², 比干净的MgB₂要高出许多,而其超导转变温度仍能维持在39.9 K的较高水平.     

Nd掺杂对Bi4Ti3O12铁电薄膜的微结构和铁电性能的影响

利用溶胶-凝胶法在Pt/Ti/SiO₂/Si(100)衬底上制备了Nd掺杂Bi₄Ti₃O₁₂(Bi_4-xNd_xTi₃O₁₂, x=0.00,0.30,0.45,0.75,0.85,1.00,1.50)铁电薄膜样品.研究了Nd掺杂对Bi₄Ti₃O₁₂薄膜的微结构和铁电性能的影响.研究结果表明:Nd掺杂未改变Bi₄Ti₃O₁₂薄膜的基本晶体结构.在掺杂量x<0.45时,Nd³⁺只取代类钙钛矿层中的A位Bi³⁺.当x=0.45时,样品剩余极化强度达最大值,在270kV·cm^-1的电场下为32.7μC·cm^-2.掺杂量进一步增加时,结构无序度开始明显增大,Nd³⁺开始进入(Bi₂O₂)²⁺层,削弱其绝缘层和空间电荷库的作用,导致材料剩余极化逐渐下降.当掺杂量x达到1.50时,掺杂离子最终破坏(Bi₂O₂)²⁺层的结构,材料发生铁电-顺电相变.     

正交LiMnO2中的重入自旋玻璃行为

用水热技术合成了单相正交LiMnO₂(o-LiMnO₂)粉末，X射线衍射表明其空间群为Pmnm.X射线衍射精修结果指出该材料存在少量的阳离子无序，但这种无序对材料的磁性没有表现出明显的影响.静态和动态的磁性研究结果表明o-LiMnO₂中存在重入自旋玻璃行为，即在T≤T_C≈118K，反铁磁态转向铁磁态，在T≤T_f≈50K，铁磁态又转向自旋倾斜玻璃态.     

1.315μm附近CO2的高分辨率吸收光谱

 利用可调谐激光长程吸收光谱测量系统，记录到1.315μm附近高气压（80kPa和40kPa）CO₂的高分辨率吸收光谱，拟合分析获得谱线参数，结果与HITRAN 2k的数据基本一致。用程差法测量了绝对吸收，氧碘激光频率(7 603.138 5cm^-1)的总吸收截面为(0.23~0.29)×^-24cm²。仅计算谱线吸收的吸收截面为0.18×10^-24cm²。在1.315μm波段COCO₂存在连续吸收，吸收截面为(0.05~0.11)×10^-24cm²。还讨论了测量误差问题。     

Gd2O3:Eu3+纳米晶的燃烧合成及光致发光性质

采用柠檬酸作燃烧剂用燃烧合成法制备了Gd₂O₃:Eu³⁺纳米晶.用X射线衍射仪(XRD)、高分辨透射电子显微镜(HRTEM)和荧光分光光度计等对Gd₂O₃:Eu³⁺纳米晶的结构、形貌和发光性能进行了分析.结果表明：不同柠檬酸与稀土离子配比(C/M)制备的样品经800℃ 退火1 h后，均得到了纯立方相的Gd₂O₃:Eu³⁺纳米晶，晶粒尺寸约为30 nm，尺寸分布较窄，其中以C/M=1.0时制备的纳米晶结晶性最好，发光强度最大.Gd₂O₃:Eu³⁺纳米晶主发射峰位置均在612 nm处 (⁵D₀→⁷F₂跃迁)，激发光谱中电荷迁移态发生红移，观察到Gd³⁺向Eu³⁺的有效能量传递.对柠檬酸与稀土离子配比(C/M)对结晶度、发光性质等的影响也进行了分析和讨论.     

Autosolitons in electron-hole plasma in p-Ge

The self-organization of an electron-hole plasma (EHP) heated by an electric field in pure p-Ge samples at T = 77 K has been studied experimentally. The derived current-voltage characteristics (CVCs) and the distributions of the electric field and IR emission of the hot carriers along the samples show that the segments of a steep rise or the S-shaped segments of the CVCs in samples with n-p junctions are related to the formation of longitudinal thermal-diffusion autosolitons (AS_‖); as a result, thin (d = 2–20 μm in diameter), melted-through current channels appear. Such AS_‖ are formed at high EHP densities (n ≥ 1 × 10¹⁶ cm⁻³), when the electron-hole scattering is dominant, and at electron temperatures T _e = (2–4.5)T ₀ (T ₀ is the lattice temperature). The saturation segments and the N-shaped segments in the CVCs are attributable to the generation of transverse thermal-diffusion high-field autosolitons (AS_⊥) in the form of narrow strata with electric field strengths = 1–20 kV cm⁻¹. High-field AS_⊥ are formed at EHP densities n = 5 × 10¹³−1 × 10¹⁶ cm⁻³, when the electron-phonon scattering is dominant, and at electron temperatures T _e ∼ Θ ≥ 5T ₀ (Θ is the Debye temperature). The generated longitudinal and transverse autosolitons have high temperatures (T _e ≥ 1000 K) and reduced carrier densities and can exist simultaneously in different parts of the sample. Original Russian Text ? M.N. Vinoslavskiĭ, P.A. Belevskii, A.V. Kravchenko, 2006, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 129, No. 3, pp. 477–492.     

Cl/HN3/I2全气相化学激光体系的化学动力学模拟计算

 对Cl/HN₃/I₂产生NCl(a)/I激光的过程进行了化学动力学计算，主要考察了Cl,HN₃和I₂的初始粒子数密度及其配比对小信号增益系数的影响。结果发现,当温度为400K, 初始Cl粒子数密度为1×10¹⁵，1×10¹⁶和1×10¹⁷cm^-3时,小信号增益系数分别达到1.6×10^-4,1.1×10^-3和1.1×10^-2cm^-1，获得最佳小信号增益系数的HN₃和I₂的初始粒子数密度分别为初始Cl粒子数密度的1～2倍和2%～4%。同时，对Cl，HN₃和I₂配比对小信号增益系数和增益持续时间的影响进行了讨论。     

SiO2分子的基态(X1A1)结构与分析势能函数

应用群论及原子分子反应静力学方法推导了SiO₂分子的电子态及其离解极限，采用B3P86方法，在6-311G^**水平上,优化出SiO₂基态分子稳定构型为单重态的C_2V构型，其平衡核间距R_e=R_Si—O=0.1587 nm,∠OSiO＝111.2°,能量为-440.4392 a.u..同时计算出基态的简正振动频率:对称伸缩振动频率ν(B₂)=945.4cm^-1，弯曲振动频率ν(A₁)=273.5 cm^-1和反对称伸缩振动频率ν(A₁)=1362.9cm^-1.在此基础上，使用多体项展式理论方法，导出了基态SiO₂分子的全空间解析势能函数，该势能函数准确再现了SiO₂(C_2V)平衡结构.     

钨酸钇钠晶体中Tm3+的光谱特性

测量了Tm³⁺:NaY(WO4)₂晶体的吸收光谱、发射光谱和激发光谱，利用J_O理论计算了钨酸钇钠晶体的强度参数：Ω₂=7.21304×10^-20cm²，Ω4=0.504766×10^-20cm²，Ω6=0.977784 ×10^-20cm²，以及Tm³⁺光学参数包括各能级的荧光寿命和荧光分支     

High-density MgB2 superconducting bulk samples prepared at ambient pressure

High-density MgB₂ (HD-MgB₂) superconducting samples (D ⩾ 2.2 g/cm³), using different sources of magnesium powder as raw material, were synthesized in ambient pressure in a rich Mg environment. The magnesium powders used in the fabrication process include nanometer-sized magnesium particles, powders from Alfa Aesar, ordinary off-the-shelf powder, and magnesium chip. The fabrication procedure involved a double-sintering process in a rich-Mg environment. A transition temperature T _c of 39 K was observed. Samples with the equally high density and matching superconducting properties were obtained as well by a triple sintering process of the MgB₂ powder directly from Alfa Aesar.      

利用电泳法在金属基底上制备MgB2超导厚膜

利用电泳技术在高熔点金属基底Ta，Mo和W上制备MgB₂超导厚膜.厚膜中的MgB2晶粒结合紧密，粒度小于1μm，呈随机取向生长.电阻测量表明沉积在Ta，Mo，W上的MgB₂厚膜的超导起始转变温度分别为36.5K，34.8K，33.4K，对应的转变宽度为0.3K，1.5K和2.0K.三种基底上制备的MgB₂厚膜的临界电流密度在不同温度下随外磁场的变化情况 基本相同，MgB₂/Mo厚膜的临界电流密 关键词： 2超导厚膜')" href="#">MgB₂超导厚膜 电泳 金属基底     

Enhanced critical current densities in Cu-sheathed MgB2

Micron-scale mixing of magnesium and boron powders by mechanical alloying allows the MgB₂ formation reaction to proceed as low as 450 °C, with high-quality material formed in an hour at 600 °C. At these low reaction temperatures the reaction can be performed in situ in a copper sheath, and it is found that the presence of copper enhances the superconducting properties of the MgB₂. Self-field critical current densities, calculated from full critical-state simulation of magnetization hysteresis, are up to 7 × 10⁵ A/cm² at 13.6 K and 1 × 10⁵ A/cm² at 30 K.     

MgB2 coated superconducting tapes with high critical current densities fabricated by hybrid physical-chemical vapor deposition

The MgB₂ coated superconducting tapes have been fabricated on textured Cu (0 0 1) and polycrystalline Hastelloy tapes using coated conductor technique, which has been developed for the second generation high temperature superconducting wires. The MgB₂/Cu tapes were fabricated over a wide temperature range of 460-520 °C by using hybrid physical-chemical vapor deposition (HPCVD) technique. The tapes exhibited the critical temperatures (T_c) ranging between 36 and 38 K with superconducting transition width (ΔT_c) of about 0.3-0.6 K. The highest critical current density (J_c) of 1.34 × 10⁵ A/cm² at 5 K under 3 T is obtained for the MgB₂/Cu tape grown at 460 °C. To further improve the flux pinning property of MgB₂ tapes, SiC is coated as an impurity layer on the Cu tape. In contrast to pure MgB₂/Cu tapes, the MgB₂ on SiC-coated Cu tapes exhibited opposite trend in the dependence of J_c with growth temperature. The improved flux pinning by the additional defects created by SiC-impurity layer along with the MgB₂ grain boundaries lead to strong improvement in J_c for the MgB₂/SiC/Cu tapes. The MgB₂/Hastelloy superconducting tapes fabricated at a temperature of 520 °C showed the critical temperatures ranging between 38.5 and 39.6 K. We obtained much higher J_c values over the wide field range for MgB₂/Hastelloy tapes than the previously reported data on other metallic substrates, such as Cu, SS, and Nb. The J_c values of J_c(20 K, 0 T) ∼5.8 × 10⁶ A/cm² and J_c(20 K, 1.5 T) ∼2.4 × 10⁵ A/cm² is obtained for the 2-μm-thick MgB₂/Hastelloy tape. This paper will review the merits of coated conductor approach along with the HPCVD technique to fabricate MgB₂ conductors with high T_c and J_c values which are useful for large scale applications.     

Effect of electron irradiation on the structure and properties of the MgB2 superconductor

This paper reports on the results of an investigation into the effect of irradiation of the Bardeen-Cooper-Schriefer superconductor MgB₂ by electrons with a mean energy ē ～ 10 MeV at low doses (0 ≤ Φt ≤ ～5 × 10¹⁶ cm^?2) on the lattice parameters, the intensity and width of diffraction lines, the superconducting transition temperature T _c , and the temperature dependence of the resistivity ρ(T) in the normal state. The results of structural investigations have revealed regularities in the defect formation in the magnesium and boron sublattices of the MgB₂ compound as a function of the electron fluence. At the initial stage, irradiation leads to the formation of vacancies, originally in the magnesium sublattice and then in the boron sublattice. For fluences Φt ≥ ～1 × 10¹⁶ cm^?2, vacancies are formed in both sublattices. The evolution of the electrical and physical properties [T _c , ρ_{273 K}, residual resistivity ratio RRR = ρ_{273 K}/ρ_{50 K}, parameters of the dependence ρ(T)] under electron irradiation is in agreement with the regularities revealed in the formation of radiation-induced defects in the crystal lattice of the MgB₂ compound.     

Microstructural and superconducting properties of C6H6 added bulk MgB2 superconductor

The effect of aromatic hydrocarbon (benzene, C₆H₆) addition on lattice parameters, microstructure, critical temperature (T_c), critical current density (J_c) of bulk MgB₂ has been studied. In this work only 2 mol% C₆H₆ addition was found to be very effective in increasing the J_c values, while resulting in slight reduction of the T_c. J_c values of 2 mol% C₆H₆ added MgB₂ bulks reached to 1.83×10⁶ A/cm² at 15 K and 0 T. Microstructural analyses suggest that J_c enhancement is associated with the substitution of carbon with boron and which also results in the smaller MgB₂ grain size. The change in the lattice parameters or the lattice disorder is claimed as a cause of the slight reduction in the T_c by carbon addition. We note that our results show the advantages of C₆H₆ addition include homogeneous mixing of precursor powders, avoidance of expansive nanoadditives, production of highly reactive C, and significant enhancement in J_c of MgB₂, compared to un-doped samples.     

Synthesis of superconductor MgCNi3 with carbon nanotubes

MgCNi3, an intermetallic compound superconductor with a cubic perovskite crystal structure, has been synthesized using fine Mg and Ni powders and carbon nanotubes （CNTs） as starting materials by the conventional powder metallurgy method. The composition, microstructure and superconductivity are characterized using x-ray diffraction （XRD）, energy dispersive x-ray （EDX） analysis, scanning electron microscopy （SEM）, and superconducting quantum interference device （SQUID） magnetometer. The results indicate that the phases of the synthesized samples are MgCNi3 （major phase） and traces of C and MgO. The MgCNi3 particle sizes range from several hundreds of nanometres to several micrometres. The onset superconducting transition temperature Tc of the MgCNi3 sample is about 7.2 K. The critical current density Jc is about 3.44 × 10^4 A/cm^2 calculated according to the Bean model from the magnetization hysteresis loop of the slab MgCNi3 sample at 5 K and zero applied field.     

Rapid preparation of Mg（B1-xCx）2 superconductor using hybrid microwave method

The crystal structure and the superconductivity for samples Mg（B1-xCx）2 （0〈 x 〈0.09） prepared by a hybrid microwave synthesis have been investigated. The starting material B10C is also obtained by using the microwave method. The carbon can distribute uniformly in the Mg（B1-xCx）2 samples because boron and carbon are mixed on an atomic scale in the staring material B10C. The dependences of both lattice parameters and superconducting transition temperature Tc on carbon content accord with those reported in the literature. The upper critical field He2 at 20 K can be enhanced from about 4.3 T for x = 0 to 10 T for x = 0.05. The critical current density Jc of Mg（B0.95 C0.05）2 is 1.05×10^4 A/cm^2 at 20 K and 1 T.