Surface atomic imaging of La2CuO4 and superconducting Tl2Ba2Ca2Cu3O10

Surface structures of the high T_c oxide superconductors Tl₂Ba₂Ca₂Cu₃O₁₀ and La₂CuO₄ have been studied by high resolution electron microscopy. In addition to the single atomic layer of La on the (113) surface observed previously, several atomic layers of the C-form of La₂O₃ were found to coat the (001) surfaces of La₂CuO₄. Surface reconstruction with the incorporation of excess Ba on the (110) surface of Tl₂Ba₂Ca₂Cu₃O₁₀ has been observed together with a stepped (11l) surface produced by a combination of the (110) and (001) planes. The (001) surface of Tl₂Ba₂Ca₂Cu₃O₁₀ was also found to terminate with a Ba-O layer. Possible mechanisms for the formation of these surface structures are discussed.     

Electrical transport and superconductivity in the Al2O3-Bi2Sr1.8Ca1.2Cu2Oy and MgO-Bi2Sr1.8Ca1.2Cu2Oy composites

We have measured the resistivities of Al₂O₃-Bi₂Sr_1.8Ca_1.2Cu₂O_y and MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y composites with the nominal Bi₂Sr_1.8Ca_1.2Cu₂O_y volume fraction, ₂₂₁₂, ranging from 0.15 to 1.00. For the Al₂O₃-Bi₂Sr_1.8Ca_1.2Cu ₂O_y composites, we find for the samples with ₂₂₁₂≥0.6 that the superconducting transition temperature, T_c, is not disturbed by the addition of Al₂O₃. For ₂₂₁₂<0.3, no zero-resistivity state is observed. For the MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y composites, T_c is barely disturbed for the samples with ρ₂₂₁₂≥0.7. No superconducting state is observed for the samples with ρ₂₂₁₂<0.35. The variation of (300 K) with ρ₂₂₁₂ indicates a three-dimensional percolating Bi-Sr-Ca-Cu-O matrix occurring at ρ₂₂₁₂≈0.19 and ≈0.15 in Al₂O₃-Bi₂Sr_1.8Ca_1.2 Cu₂O_y and MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y, respectively. Both resistivity and magnetization measurements suggest that the reactions of Bi₂Sr_1.8Ca_1.2Cu₂O_y with MgO are weaker than with Al₂O₃.     

The flux jumps in high TcBi1.7Pb0.3Sr2Ca2Cu3Oy bulk superconductor

There was giant flux jumps in high Tc Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O_y bulk superconductor. The relaxation time, τ, decreased with both the increase of magnetic field and the rise of temperature. The maximum τ was about 40 min.. The average-dM/dt increased with both the increase of magnetic field and the rise of temperature. The minimum average-dM/dt was about 4.1×10⁻²G/min.. The flux jump weakened with time. It was dependent on the decrease of gradient of magnetic flux density dn/dx in the sample.     

Electrochemical reduction of Bi2Sr2Ca1Cu2O8 superconductor single crystals

Single crystals and polycrystalline pellets of the high-temperature cuprate superconductor Bi₂Sr₂Ca₁Cu₂O₈ were doped at room temperature by electrochemical reduction at > 95% Coulombic efficiency using lithium dopant ions in propylene carbonate electrolyte. Cyclic voltammetry and potential step measurements on single crystals suggest an unusual reduction mechanism, with a diffusion coefficient for Li⁺ in the c-axis direction of bulk superconductor of ca. 3 × 10⁻¹¹ cm²s⁻¹. Sintered pellets of polycrystalline powder could be doped more rapidly, with an apparent diffusion coefficient of 7 × 10⁻⁸ cm²s⁻¹. X-ray susceptibility analysis show extensive disordering occurs on heavy Li doping, with a first-order transition from a crystalline/superconducting to an amorphous/non-superconducting phase. Single, crystals of Bi₂Sr₂Ca₁Cu₂O₈ exhibited a color change on reduction from metallic gray to golden bronze. The reduced material was highly air-sensitive, forming a hydroxide surface film on exposure to ambient atmosphere.     

BaO-Li2O-B2O3三元系中BaB2O4-Li2B2O4和BaB2O4-Li2O截面相平衡关系的研究

本文用X射线和差热分析方法对BaO-Li₂O-B₂O₃三元系中的两个截面:BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O作了研究。在BaB₂O₄-Li₂B₂O₄赝二元系中发现了一个新的化合物4BaB₂O₄·Li₂B₂O₄。化合物在930±3℃由包晶反应形成,并与Li₂B₂O₄形成共晶反应。共晶温度为797±3℃,共晶点组分为79mol％Li₂B₂O₄。在BaB₂O₄-Li₂O截面中也存在化合物4BaB₂O₄·Li₂B₂O₄,其包晶反应温度从930±3℃随Li₂O含量增加下降到908±3℃。在组分60mol％Li₂O处形成另一个新的化合物2BaB₂O₄·3Li₂O。该化合物在630±3℃也是由包晶反应形成,并与Li₂O和Li₂CO₃分别形成共晶反应,共晶温度分别为400±3℃和612±3℃。在BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O体系中都没有观察到固溶体。用计算机程序分别对化合物4BaB₂O₄·Li₂B₂O₄和2BaB₂O₄·3Li₂O的X射线粉末衍射图案进行了指标化,其结果:4BaB₂O₄·Li₂B₂O₄的空间群为Pmma,a=13.033?,b=14.630?,c=4.247?,每个单胞包含两个化合式单位;2BaB₂O₄·3Li₂O的空间群为Pmmm,a=4.814?,b=9.897?,c=11.523?,每个单胞也含有两个化合式单位。 关键词：     

Bi2Pb2V2O10的晶体结构

使用X射线单晶衍射法测定了Bi₂Pb₂V₂O₁₀的结构。该晶体属三斜晶系,空间群为C₁¹-P1,单位晶胞内化学式数Z=1,晶胞参数为:a=7.084(4)?,b=7.278(3)?,c=5.587(3)?,α=111.91(5)°,β=95.01(6)°,γ=108.86(4)°,V=245.70?³,D_x=7.35g/cm³,μ(MoK_α)=678,94cm^-1,F(000)=456。用Patterson函数分析及Forier技术测定了结构,对原子坐标、各向同性及各向异性热参数进行了最小二乘方修正,R=0.079。结构分析表明,Bi₂Pb₂V₂O₁₀的Pb原子与O原子形成八角十二面体,Bi原子与O原子形成六角多面体。两个共棱的Pb—O多面体与两个共棱的Bi—O多面体相连,并沿bc平面无限延伸。讨论了吸收的影响。最后,将Bi₂Pb₂VO₁₀的结构与Pb₂SO₅的结构进行了比较。 关键词：     

钙钛矿(C6H5CH2NH3)2PbBr4拉曼光谱研究

运用激光拉曼光谱实验和密度泛函理论计算研究了450～1 700 cm-1光谱范围内有机-无机杂化钙钛矿材料(C₆H₅CH₂NH₃)₂PbBr₄的振动模式特性。对比实验所得拉曼光谱和理论计算所得拉曼光谱,发现密度泛函理论计算可以很好的模拟(C₆H₅CH₂NH₃)₂PbBr₄有机部分的分子振动模式。同时通过比较分析密度泛函理论计算和参考文献,对450～1 700 cm-1光谱范围内的拉曼峰的分子振动模式进行了初步的归属,并发现该光谱范围内的拉曼峰主要是由(C₆H₅CH₂NH₃)₂PbBr₄分子中有机部分振动所产生的。     

Superconductivity at 30 K in the Nd2CuO4-type cuprate Tm1.83Ca0.17CuO4

The Nd₂CuO₄-type Ca-doped rare-earth cuprates R_1.83Ca_0.17CuO₄ (R=Gd, Dy or Tm) have been synthesized under high pressure. Only that with the small ion Tm³⁺ and thus the short Cu---O bonds (1.916 Å) was superconducting (at about 30 K). This was considered to be the first example of p-type superconductivity in the purely square-planar CuO₂ layers without apical oxygens.     

Angle-resolved photoemission study of nonsuperconductive Bi2Sr2Ca0.4Y0.6Cu2O8

A comparative angle-resolved photoemission measurement has been performed on nonsuperconductive Bi₂Sr₂Ca_0.4Y_0.6Cu₂O₈ and superconductive Bi₂Sr₂CaCu₂O₈ to study the nature and origin of the electronic states near the Fermi level. It was found that hole-doping does not cause a rigid shift of the density of states relative to the Fermi level, but creates new electronic states in the vicinity of the Fermi level.     

Solid-state electrochemical CO2 sensor by coupling lithium ion conductor (Li2CO3-Li3PO4-Asl2O3) with oxide ion-electron mixed conductor (La0.9Sr0.1MnO3)

A solid-state electrochemical cell of the type O₂(air), PtLa_0.9Sr_0.1MnO₃/Li₂CO₃(+5 mol% Li₃PO₄ + 6 mol% Al₂O₃)/Au, CO₂, O₂ was composed to determine CO₂ concentration, where Li₂CO₃, a lithium ion conductor, was used as an electrolyte, and the perovskite-type oxide (La_0.9Sr_0.1MnO₃)/O₂-electrode as a reference electrode. The electromotive force (EMF) of the cell was found to be proportional to the logarithm of CO/₂ partial pressure in CO₂/O₂/N₂ gas mixtures at temperatures between 300 and 400 °C. The EMF responded to changes of CO₂ partial pressure within 1 min at 400 °C. The sensitivity to CO₂ of this cell was not affected by coexistence of O₂, and the EMF remained constant after the first 15 days. The mechanism for sensing CO₂ is discussed.     

ArF laser-induced discharge interruption in a mixture of C2H3Cl/CF4/CH4, CF4/CH4, and C2H3Cl/He

The ArF-laser (193-nm)-induced discharge interruption is comparatively described in a mixture of C₂H₃Cl/CF ₄/CH₄, CF₄/CH₄, and C₂ H₃Cl/He using a hollow-cathode-type discharge tube. The unfocused ArF laser (typically 27 mJ/cm² and 10 ns duration) illuminated both the negative glow inside the hollow cathode and the column between the two electrodes. With a 1.8-torr mixture of C₂ H₃Cl/CF₄, the discharge current of 1 mA was decreased rapidly with a current-decay time constant of 1 μs and a current-decay rate of 1 kA/s. With a 1.5-torr mixture of CF₄/CH₄, 2.2 μs and 450 A/s were obtained. With a 1.5-torr mixture of CH₂H₃Cl/He, a time constant of over 3 μs and a rate of less than 300 A/s were obtained. An analysis of the discharge interruption induced by ArF-laser irradiation is given in terms of photon-plasma kinetics. The current peak induced by ArF irradiation is also explained for a mixture of C₂H₃ Cl/He in terms of photoionization and photodetachment processes     

High-resolution electron microscopy study of Ni81Fe19 film with Co33Cr67 buffer layer

The anisotropic magnetoresistance (AMR) in permalloy Ni₈₁Fe₁₉ film deposited on a 1.2 nm Co₃₃Cr₆₇ buffer layer was significantly enhanced. The high-resolution electron microscopy was used to study the microstructure of Ni₈₁Fe₁₉ film with and without Co₃₃Cr₆₇ buffer layer. It was found that Co₃₃Cr₆₇ buffer layer can induce good (1 1 1) texture, while without Co₃₃Cr₆₇ buffer layer, Ni₈₁Fe₁₉ film show randomly oriented grain structure. The Δρ/ρ enhancement is attributed to the decrease in the resistivity ρ of the Ni₈₁Fe₁₉ film due to the formation of the large (1 1 1) textured grains in Ni₈₁Fe₁₉ film with Co₃₃Cr₆₇ buffer layer. However, the surface roughness of substrate may limit the (1 1 1) textured grain size and induce additional grain boundaries in Ni₈₁Fe₁₉ film with Co₃₃Cr₆₇ buffer layer, limit the enhancement of the AMR effect.     

Lithium insertion into Li4V3O8

The lithium insertion characteristics of lithium vanadate, Li₄V₃O₈, were investigated using LiV₃O₈ prepared by the precipitation technique as the starting material. The Li₄V₃O₈ phase was formed by lithiation over x=1.5 in Li_1+xV₃O₈, and the diffusion of lithium in this phase determined the reaction rate of insertion more than x=1.5. Improvement of insertion kinetics in the Li₄V₃O₈ phase extended the lithium insertion limit from x=3.2 to x=4.0, compared with the case of LiV₃O₈ by conventional high temperature synthesis. Lithium insertion proceeds as the single-phase reaction in the range of 3.2<x<4.0.     

Curie temperatures of Y3Fe5O12/Gd3Fe5O12 superlattices

The magneto-optical Kerr effects (MOKE) of epitaxial Y₃Fe₅O₁₂/Gd₃Ga₅O₁₂ (YIG/GGG) garnet superlattices grown on (1 1 1)GGG previously by pulsed laser deposition (PLD) were measured. A series of superlattices were investigated with the thickness of the ferrimagnetic YIG layer varied from six unit cells to only one unit cell while keeping the Curie paramagnetic GGG fixed at one unit cell. It was demonstrated that the ellipsometric technique employing photoelastic modulators (PEM) is sensitive enough to measure the MOKE signals of these ultrathin oxide samples. The Curie temperatures, determined by MOKE, are fit with a power law, yielding a shift exponent λ = 3.1 ± 1.2.     

水热体系TeO2-K3PO4-H2O中一个新化合物——K2Te4O9·3H2O的合成与结晶

作者用水热法对TeO₂-K₃PO₄-H₂O体系作了初步的合成与结晶尝试。在给定的条件和组成范围内除了能形成TeO₂晶体外,还能生成一种点阵参数为a=b=10.734?,c=21.041?,α=β=90°,γ=120°的三方晶系的化合物γ,其分子式为K₂Te₄O₉·3H₂O。结晶区的产物主要取决于原料的k=TeO₂/K₃PO₄(克分子比:当k≤1.9时,仅生成γ晶体;k≥2.22时,单独生成TeO₂晶体;而当1.92晶体出现,本文还给出了γ晶相的DTA曲线和X射线粉末衍射谱线的相对强度与相应面间距的详细数据。 关键词：     

Infrared optical response of YBa2Cu3O7 and PrBa2Cu3O7 An ellipsometric study

Ellipsometry was used to study (110) and (001) oriented films of YBa₂Cu₃O₇ and PrBa₂Cu₃O₇ in the mid-and near-infrared spectral regions. Below a photon energy of 0.1 eV, the in-plane component of the dielectric tensor of YBa₂Cu₃O₇ is dominated by a Drude term with a squared plasma energy of (3.0 ± 0.3) eV². This “oscillator strength”, and the Lorentzian broadening energy of (0.104 ± 0.005) eV at room temperature, are confirmed by the changes induced in Pr-substituted material, and by low-temperature measurements in the near-infrared. The deviation from the Drude behavior observed above 0.1 eV is accounted for by a broad absorption band with an oscillator strength of (3.6 ± 0.1) eV² in YBa₂Cu₃O₇ which shifts to higher energies and takes over almost all of the oscillator strength of the Drude term when Y is substituted by Pr. The response to electric fields perpendicular to the planes is much weaker, with an upper bound of 0.63 eV² for the squared plasma energy. The in-plane loss function computed from the measured dielectric function follows the Drude-like lineshape, modified by the bound-state absorption band, down to the lowest energy reached in our measurements (0.058 eV).     

Ce3+掺杂SiO2-Al2O3-Gd2O3玻璃的闪烁性能

通常, Ce离子掺杂的低密度玻璃有较高的发光效率, 而高密度的Ce离子掺杂玻璃其发光效率很低. 为了解释这一现象, 采用高温熔融法获得了SiO₂-Al₂O₃-Gd₂O₃三元系统的玻璃形成区, 并在还原气氛下制备了Ce³⁺掺杂SiO₂-Al₂O₃-Gd₂O₃以及SiO₂-Al₂O₃-Gd₂O₃-Ln₂O₃ (Ln=Y, La, Lu)闪烁玻璃, 研究了其光谱和闪烁性能. 测试结果显示: 随着Gd₂O₃含量增加, 玻璃紫外截止波长发生红移, 荧光强度降低, 衰减时间缩短; 加入Lu₂O₃, La₂O₃, Y₂O₃后, 紫外截止波长发生红移, 荧光强度降低, 衰减时间变短; 当Gd₂O₃超过10% mol时, X射线荧光积分光产额从相当于锗酸铋 晶体的61%降低到13%. 荧光强度降低、衰减时间缩短的原因是随着玻璃的紫外截止波长红移玻璃的能带宽度变窄, 使得Ce³⁺离子的d电子轨道开始接近玻璃的导带, Ce³⁺离子受辐射后跃迁到d电子轨道的电子会通过导带与玻璃中的空穴复合, 产生电荷迁移猝灭效应.     

Crystal structure of Tl0.5Pb0.5Sr2Ca2Cu3O9 at 300 K and around Tc (118 K)

The crystal structure including the cation distribution, of a polycrystalline sample of nominal composition Tl_0.5Pb_0.5Sr₂Ca₂Cu₃O₉ with T_c = 118.2 K has been determined using resonant synchrotron X-ray diffraction data collected at the Cu K, Tl L_III and Sr K edges and time-of-flight powder neutron diffraction data. No oxygen deficiency was observed, but cation disorder at all the non copper sites according to the formula (Tl_0.60Pb_0.40)(Sr_1.60Ca_0.40)(Ca_1.93Tl_0.07) Cu₃O₉ gives a mean hole concentration of 0.18(1) per Cu atom for the three CuO₂ planes, consistent with the high T_c for this material. Analysis of five time-of-flight powder neutron diffraction data between 80 and 150 K have revealed a possible discontinuity in the variation of the c lattice parameter at T_c, due to an anomaly in the position of the apical oxygen atoms.     

Intergrain and intragrain superconductivity in Sn- and Sb-doped Bi1.7Pb0.3Sr2Cu3Oy

Measurements of the resistivity and current dependent resistivity for small current densities ranging from 0.03 A/cm² to 3.0 A/cm² were performed with two Sn-doped and two Sb-doped polycrystalline Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O_y samples in magnetic fields up to 1.7 T. Features in the temperature derivative of the resistivity curves were associated with the presence of a superconducting transition between superconducting grains, coupled by weak links with a distribution of critical currents and critical temperatures, and the superconducting transition within grains. The transition between grains was more strongly suppressed in temperature with the application of a magnetic field in samples with weaker coupling between grains. The presence of a transition in a magnetic field due to weak links between grains was verified at 77 K by the observation of a current dependent resistivity in a magnetic field.     

(NH4)2SO4，NH4NO3和(NH4)2SO4/NH4NO3混合气溶胶吸湿质量增长因子的快速测量方法

气溶胶颗粒的吸湿性决定了其尺寸、浓度、化学组成以及相态,从而显著影响着全球气候、大气异相化学以及人类健康。运用在线、原位、连续扫描衰减全反射傅里叶变换红外光谱（ATR-FTIR）技术, 结合线性湿度（RH）控制系统,实现了RH连续变化条件下气溶胶FTIR-ATR光谱的快速测量。根据水弯曲振动谱带（~1 640 cm-1）峰面积随RH的变化,得到了(NH₄)₂SO₄,NH₄NO₃和(NH₄)₂SO₄/NH₄NO₃混合气溶胶的质量增长因子（MGFs）、潮解点（DRH）和风化点（ERH）。与气溶胶的E-AIM模型预测值相比较,实验结果表现出良好的一致性,证实该方法是一种测量大气气溶胶MGFs,ERH和DRH的快速测量方法。