Fluorination of superconducting Ba2YCu3O9−δ

Using a series of samples ranging in composition from δ = 2 to δ = 3 we have successfully introduced substantial amounts of fluorine into samples of superconducting Ba₂YCu₃O_9-δ by annealing under F₂ gas flows at low temperatures. These syntheses yielded single phase materials containing up to 1.05 F per formula unit. ¹⁹F NMR experiments have confirmed that fluorine is incorporated into the lattice and susceptibility and transport measurements indicate that the samples are superconducting with critical temperatures in the range 80 to 89 K.     

Electron microscopy and neutron diffraction studies of Ba2YCu3O7−δ compounds

An electron microscopy study of Ba₂YCu₃O_7−δ samples gives evidence of several defects occuring in the stacking sequence along the c axis. It is shown that the oxygen intercalation process is reversible and does not change these defects of the cation lattices.A neutron diffraction study of powdered samples indicates that the oxygen-rich compounds Ba₂YCu₃O_6.92 and Ba₂YCu₃O_6.64 have the same orthorhombic structure, the only difference consisting in the occupancy of the oxygen site around the copper atoms forming linear Cu-O chains. The reduced compound Ba₂YCu₃O₆ has a tetragonal structure corresponding to an empty oxygen site in the plane of these copper atoms. The contraction of the c parameter and of the volume of the unit cell when the oxygen content increases can be explained by the electrostatic attraction between Ba²⁺ and O²⁻ ions introduced in the lattice.     

循环伏安法研究Ba2YCu3O7—y超导体

本文利用电化学循环伏安法(CV 法),以饱和 Ba(OH)_2水溶液为电解液,对单相Ba_2YCu_3O_(7-y)正交和四方结构超导体进行了研究.结果发现:在典型的正交相中确实存在Cu~(3+)→Cu~(2+)的还原峰,而四方相则无此峰出现.从而首次直接检测到 Ba_2YCu_3O_(7-y)烧结体中 Cu~(3+)离子.     

Transport properties in single phase superconductor Ba2YCu3O9-δ

The electrical resistivity and the thermopower are measured on the single phase superconductor Ba₂YCu₃O₉-δ (δ=2.1). The results indicate that the temperature dependences of the resistance and thermopower exhibit typical metallic behaviour, and the sample conducts via electrons at high temperatures. The behaviour of the thermopower can be described with Mott's semi-classical model. The specific heat of electrons in normal state has been estimated 780mJ/K·mole at 200K, i.e. γ=3.9mJ/K²·mole. Unusual phonon-drag effect is observed above the superconducting transition temperature T_c. Below T_c, the electrical resistivity and the thermopower all drop to zero corresponding to a superconducting ground state.     

High-temperature superconductor Ba2YCu3O7-¢L: plasmon and ultraviolet optical transition studies

We present the first electron energy loss data on a high-temperature superconductor. A detailed comparison with photoemission energy distribution curves and partial-yield spectra identifies the nature of the corresponding features. This analysis shows that the bulk plasmon energy is 24.6 eV, and that there are two peaks in the density of empty states, 2.3–2.5 eV and 4.3–4.6 eV above the Fermi level.     

The vacancy order — disorder transition in Ba2YCu3O7−δ observed by means of electron diffraction and electron microscopy

It is shown by means of electron microscopy and electron diffraction that the “structural” vacancies in Ba₂YCu₃O_7−δ undergo an order-disorder transformation accompanied by a change in symmetry from orthorhombic to tetragonal. A superstructure due to the ordering of vacancies was found in certain crystal parts; it leads to doubling of the a₀ parameter. It is shown that the ordering of the vacancies is important for the superconducting behaviour. In order to obtain a high T_c supraconductor the final heat treatment is crucial.     

Heavy atom disorder in the high Tc superconductor Ba2YCu3O7−δ studied by means of electron microscopy and electron diffraction

It is shown that on rapid cooling of the compound Ba₂YCu₃O_7-δ one obtains a highly disordered material in which the perovskite framework is conserved but in which barium and yttrium atoms exhibit a high degree of disorder. This leads to lattice deformations, which can be visualized in the electron microscope. The electron diffraction patterns also reveal the disorder. As-quenched specimens are no longer high T_c superconductors, but the superconducting properties can be recovered by an adequate heat treatment whereby the vacancies become ordered.     

Structural Transformations in a Bi2O3 Crystal and in Bi2O3‐Based Solid Solutions in the Temperature Interval 25–750°C

The Raman scattering spectra of isostructural Bi₂O₃ and Bi_1.8Tm_0.2O₃ in the course of heating have been investigated. It is shown that the sequences of structural changes with increase in temperature differ: and ^* , respectively. In the hightemperature region, the structure takes the form of a disordered cube irrespective of the previous history of specimens.     

Righi-Leduc Effect in InSb between 25°C and 300°C

The Righi-Leduc effect has been measured for n-type InSb crystals of various mobilities and was found to increase with temperature in a manner to indicate that the unipolar contribution is prevalent over the bipolar part of the effect. The experimental values measured over the temperature range between 25°C and 300°C agree well withPutley's theory. The Righi-Leduc coefficient was also determined as a function of the magnetic field and the strong decrease observed is explained in terms of the magnetoresistance.     

Transport properties and high Tc superconductivity in single phase Ba2DyCu3O7−δ

Results of resistivity, ac magnetic susceptibility, Hall effect and superconducting transition temperature measurements for single phase Ba₂DyCu₃O_7−δ are reported. The positive value of the Hall coefficient indicates than in the normal state the material conducts via holes with a carrier concentration of 1.0×10²¹cm^-3. A large anomaly in R_H near T_c is observed.     

Electrical and magnetic properties of Gd(Ba2-xLax)Cu3O7+δ

We have studied the structural, electrical, and magnetic properties of the normal and superconducting states Gd(Ba2-xLax)Cu3O7+ [Gd(BaLa)123] samples with 0.0 x 0.8 prepared by the standard solid-state reaction. XRD characterization shows an orthorhombic-tetragonal structural transition at x=0.2. Iodometric titration analysis shows the oxygen content of the samples increase with the increase of La doping. The resistivity curves show that for x0.15, there is metallic behavior, and for x0.2, there is a gradual insulating transition behavior in the normal state. The metal-insulator and superconductor-insulator transitions occur between x=0.35 and x=0.4. The superconducting transition temperature decreases with the increase of La content as two-step curve. The normal-state resistivity is fitted for two and three dimensional variable range hopping (2D&3D-VRH) and Coulomb gap (CG) regimes, separately. The results show that the dominant mechanism is CG for x0.35, and VRH for x0.4. The pinning energy U, derived from the thermally activated flux creep (TAFC) model and Ambegaokar-Halperin (AH) theory, shows a power-law relation as UH -. The critical current density decreases with the increase of La doping and magnetic field. The E-J curves show that the induced electric field increases with the increase of magnetic field and La concentration. The magnetization measurements indicate that the critical penetration fields and magnetic current density decrease with La doping.     

Synthesis of smooth and superconducting (Cu, C)–Ba–O/CaCuO2/(Cu, C)–Ba–O films using SrCuO2 buffer

Artificially stacked structures of [(infinite layer CaCuO₂)_k/(superconducting (Cu, C)Ba₂CuO_x:(Cu, C)-1201)_l]_m were fabricated on SrCuO₂ buffer layer by means of sequential deposition of each block using pulsed laser deposition. Smooth and epitaxial growth all over the deposition cycles of (Cu, C)-1201 and CaCuO₂ were confirmed by streak patterns of in situ RHEED. In comparison with (Cu, C)-1201 single layer films, the artificial stacking resulted in a rise of superconducting properties, T_c-onset and T_c(ρ=0) up to 95 K and 65 K, respectively.     

700～85°C内H2O对CaO上NH3氧化的影响

本文验证了先前建立的FTIR定量方法对高H2O含量下NO和NH3测量的精度,研究了700～850°C内H2O对CaO上NH3氧化的影响.结果表明:含H2O高达15%时,NO和NH3的测量结果仍具有高精度,误差分别为±2%和±3%;H2O抑制CaO上NH3氧化的活性及副产物NO2的生成;NH3转化率随H2O浓度增大先迅速降低而后降低缓慢;同一温度下,NO产物选择性不随H2O浓度变化而改变;基于H2O Langmuir吸附于CaO表面竞争活性位,建立了H2O抑制CaO上NH3氧化的动力学模型,与实验结果符合良好.     

Specific Features of the Local Structure and Transport Properties of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 Crystals

Optics and Spectroscopy - The specific features of the local structure of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 crystals are revealed by optical spectroscopy using the Eu3+...     

Low temperature structure of FeSr2YCu2O6+δ magnetic superconductor

FeSr₂YCu₂O_6+δ with the tetragonal Ba₂YCu₃O_6+δ-type structure exhibits superconductivity around 60 K, when it is properly annealed in N₂ and subsequently in O₂. This compound also exhibits antiferromagnetic order of Fe around 20 K. We have performed neutron powder diffraction of the FeSr₂YCu₂O_6+δ system at low temperature to investigate the relation between the crystal structure and the physical properties. Neutron diffraction study indicates that this compound does not have the structure phase transition due to the tilt of the FeO₆ octahedron differently from the RuSr₂GdCu₂O₈ magnetic superconductor with the same structure, and that the magnetic order in FeSr₂YCu₂O_6+δ is not long-range order, because we can observe no extra reflection due to the crystal and magnetic superstructure.     

The fluorescence and thermoluminescence characteristics of α-Al2O3:C ceramics

This paper reports that polycrystalline α-Al₂O₃:C ceramics are fabricated by conventional ceramics process. The excitation, emission spectra, thermoluminescence (TL) and optical stimulated luminescence (OSL) of α-Al₂O₃:C polycrystalline ceramics are investigated. There exists 410nm maximum emission peak which is caused by recombination of an electron with F⁺ centre to produce an excited F centre. The samples show three clear TL glow peaks at 405, 493 and 610K. The attenuation constant of exponentially decaying fast component (τ₁) and slow component(τ₂) of OSL curve are 8.43s and 41.73s, respectively. Those fluorescence and thermoluminescence characteristics are similar with α-Al₂O₃:C crystal.