高温超导体制备条件的人工神经网络识别

高温超导体的制备条件要求严格,其掺杂量大小、烧结温度控制等都直接影响实验样本的超导性质。近几年高温超导研究已积累大量实验数据,如何应用人工智能方法处理这些数据寻找更好的合成条件颇有意义。人工神经网络方法在许多领域己显示其处理复杂数据和模式识别的优越性,但尚未应用到化合物制备研究方面。本文对此作了初步尝试。     

The driving torque of a rotating levitated cylindrical permanent magnet above a superconductor

Due to the Meissner effect, a permanent magnet is levitated, when released above a high temperature superconductor. When there is an inhomogeneous temperature field around the magnet, the magnet might start to oscillate with increasing amplitude until it remains in a continuous rotation. A mathematical model for the described effect is presented which couples heat transfer and electromagnetic forces with the equation of motion, yielding to a multiphysics task. In a detailed analysis it is found, that the torque which drives the rotation of the magnet, is explicitly given in terms of Bessel functions and the Fourier coefficients of order zero and one of the temperature field of the surrounding air.     

ESTIMATE OF THE UPPER CRITICAL FIELD AND CONCENTRATION FOR SUPERCONDUCTOR

The effect of an applied magnetic field on an inhomogeneous superconductor is studied and the value of the upper critical magnetic field Hc3 at which superconductivity can nucleate is estimated. In addition, the authors locate the concentration of the order parameter, which depends on the inhomogeneous term a(x). Unlikely to the homogeneous case, the order parameter may concentrate in the interior of the superconducting material, due to the influence of the inhomogeneous term a(x).     

利用电子束蒸发制备铝隧道结工艺研究

采用电子束蒸发的方法在Si片上制备超导铝(Al)薄膜。利用X射线衍射和直流四电极电阻法分别测试了厚度从100埃到5000埃的Al薄膜物向组成,超导转变温度(Tc)和临界电流密度(Jc)。当Al薄膜厚度大于500埃时,超导转变温度Tc=1.2K。电子束蒸发制备的Al薄膜性能良好,具有较高的结晶质量,为制备Al超导隧道结奠定了良好基础。对小面积的Al超导隧道结工艺进行了研究,该超导隧道结两层的超导体材料为Al薄膜,中间势垒层材料为Al2O3。其中Al薄膜利用电子束蒸发制备,势垒层通过直接氧化Al薄膜表面实现,该工艺和采用直接蒸发氧化物薄膜工艺相比不仅简单而且能有效防止势垒层不连续造成的弱连接。     

ICP-AES测定铋系超导材料中各金属元素含量

建立了ICP-AES同时测定铋系超导材料中Bi、Pb、Sr、Ca、Cu5种金属元素含量的分析方法,优化了仪器的最佳工作条件。该方法无需复杂的前处理,没有谱线和基体干扰,检出限Bi为0.01699μg.mL^-1、Pb为0.02121μg.mL^-1、Sr为0.002854μg.mL^-1、Ca为0.007401μg.mL^-1、Cu为0.003726μg.mL^-1。该法相对误差均小于1.0%,RSD均小于1.0%,简便,快捷,完全满足铋系超导材料中各元素含量的测定。     

Formation of metallic NbSe2 nanotubes and nanofibers

We succeed in synthesizing NbSe₂ nanotubes along with nanofibers by chemical vapor transportation. They are stable crystalline systems and can be synthesized reproducibly in a nearly equilibrium reacting process. We have investigated these nanosize structures of NbSe₂ by transmission electron microscopy and electron diffraction. Both of the structures have a similar size of 100–200 nm in diameter. While nanotubes consist of rolled-up NbSe₂ layers, nanofibers are a pile of thin flat layers. We propose a mechanism of the formation of NbSe₂ nanotubes and nanofibers on the basis of deseleniditive transition from a NbSe₃ fiber-shaped crystal. We also measured electrical resistance of the nanofibers with conductive atomic force microscopy and demonstrated that the material show metallic behavior at room temperature.     

30M-35kV/2000A高温超导电缆制冷系统

本文介绍了我国新研制成的首条并网运行的热绝缘型30M-35KV/2000A高温超导电缆制冷系统。该制冷系统主要有液氮泵箱、过冷箱、高真空输液管道、液氮贮槽、辅助减压抽空系统、泵箱及气动阀门供气系统、监控系统所组成。冷却方式是过冷液氮循环,制冷方式是G-M制冷机和减压抽空(备用)。给出了制冷系统的运行结果。     

Anisotropic thermoelectric and superconducting properties of the bulk misfit-layered (SnSe)1.17(TaSe2) compound

We present the thermoelectric and superconducting properties of the bulk misfit-layered (SnSe)_1.17(TaSe₂) compound with the critical temperature (T_c ~ 3.8 K). From XRD and electrical resistivity, the anisotropic properties of the misfit-layered compound by the preferred orientation were observed. The zero-temperature-limit upper critical field H_c2(0) and coherence length ξ are obtained by H_c2(0) = 8.94 T and ξ = 6.1 nm. The electron-phonon coupling constant (λ_e-p = 0.735) and the specific heat jump (ΔC_e/γT_c ~ 1.4) imply that the (SnSe)_1.17(TaSe₂) compound is a weak coupled conventional s-wave superconductor. Density functional theory (DFT) calculation results show that some electronic charge transfers from the SnSe layers into the TaSe₂ layers. In addition, the thermoelectric properties of the bulk misfit-layered (SnSe)_1.17(TaSe₂) compound show significant anisotropic properties.     

分光光度法测定铋系超导材料中钙

在pH=10.6的NH3-NH4Cl缓冲溶液中,钙离子和酸性铬蓝K显色,于498nm波长处以试剂空白作参比,测定该显色液的吸光度。建立了铋系超导前驱粉(Bi2Sr2Ca2Cu3Ox)中直接测定钙含量的方法。试样中大量存在的锶不干扰测定,用柠檬酸溶液作掩蔽剂,消除了铜的干扰。ε=9.0×103L·mol-1·cm-1,Ca在0—50μg·25mL-1范围内吸光度和浓度有良好的线性关系,回归系数r=0.9994。对合成样品进行6次测定,相对误差为-0.93%。对两种实际样品分别进行6次测定,RSD分别为1.63%和1.19%。     

YBa2Cu3O7-δ/La0.6Pb0.4MnO3多层膜的制备及激光感生热电电压效应的研究

采用脉冲激光沉积法在倾斜LaAlO3(100)衬底上制备了(YBa2Cu3O7-δ/La0.6Pb0.4MnO)L(L为多层膜周期数)外延多层膜.X射线衍射谱显示(YBCO/LPMO)L多层膜沿c轴生长.观察到多层膜中有很大的激光感生热电电压(LITV)出现,与YBa2Cu3O7-δ(YBCO)和La0.6Pb0.4MnO3(LPMO)单层膜相比,多层膜的LITV信号有约一个数量级的增强.讨论了影响(YBCO/LPMO)L多层膜的LITV效应的因素.