SrCe0.95 Yb0.05 O3-α的制备及其质子导电特性

利用固相反应法制备出固态质子导体SrCe0 .95Yb0 .0 5O3 -α,并使用X射线衍射分析法及低频阻抗测量法对其电子结构和导电特性进行了研究 .X射线分析结果表明 ,该物质为钙钛矿晶体结构 ,具有p型电子空穴和氧离子空穴 .在低温下主要为电子导电 ,且电子导电率随温度的升高而增大 .在含氢气环境中 ,当温度高于 5 5 0K时 ,SrCe0 .95Yb0 .0 5O3 -α具有明显的质子导电性 ,随着温度的升高 ,质子导电性增强 .当温度高于 80 0K时 ,质子是导体中的主要载流子 ,质子电导率可达 4 .5mS/cm .     

Mechanical characterization of melt-textured Y0.95Er0.05Ba2Cu3O7−δ superconductor prepared in air

The effect of Er substitution on the mechanical properties of ab- and a(b)c-planes of melt-textured YBa₂Cu₃O_7?δ is reported in the present work. The non-oxygenated samples were characterized by scanning electron microscopy, X-ray diffraction and mechanical properties by instrumented indentation and conventional Vickers indentation whereas the superconducting properties were determined by resistivity measurements on oxygenated samples. The X-ray pattern and EDS analysis revealed the presence of Y-123, Y-211 and BaCeO₃ phases. Er substitution up to 5 wt.% did not affect the superconducting properties. No difference in hardness was observed for the ab- and a(b)c-planes. Elastic modulus of the a(b)c-plane was 10% higher than of the ab-plane. Differences in indentation fracture toughness obtained by conventional Vickers indentation of the ab- and a(b)c-planes was observed. The addition of 5 wt.% of Er did not affect significantly the mechanical properties of melt-textured samples when compared with pure melt-textured YBa₂Cu₃O_7?δ.     

Process of magnetic field penetration into the high-temperature superconductor YBa2Cu3O7−δ

The processes of magnetic field penetration into the ceramic samples of the HTSC YB₂Cu₃O_～6.95 at T<T _c are studied by the methods of internal friction and magnetization measurements. A clearly manifested correlation is observed between the field dependences of the internal friction spectrum parameters (the logarithmic damping decrement Q ^?1 and the resonance frequency f) and the trapped magnetic flux ΔM. The magneto-mechanical approach we used reveals a significant difference in the field dependences of the densities of pinned (N _p) and free (N _f) Abrikosov vortices for H>H _c1.     

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.     

Structural and superconducting properties of Eu1−xPrxBaSrCu3O7−δ

We have investigated the structural and superconducting properties of Eu_1−xPr_xBaSrCu₃O_7−δ by X-ray diffraction analysis, AC and DC magnetization and DC resistivity measurements. The parent compound crystallizes in the orthorhombic symmetry which transforms to tetragonal symmetry at x=0.2. Superconducting transition temperature T_c decreases monotonically with increasing x which approaches zero at x=0.6. The enhancement in critical concentration x_cr observed in Eu_1−xPr_xBa₂Cu₃O_7−δ on replacing 50 at.% Ba by Sr is attributed to the resulting local structural changes.     

Elastic properties of superconducting and non-superconducting DyBaSrCu3O7−δ

Ultrasonic longitudinal and shear wave velocities were measured for superconducting and non-superconducting DyBaSrCu₃O_7−δ (Dy-1113) at 10 MHz between 80 and 270 K. The superconducting sample exhibits a step-like elastic anomaly between 190 and 230 K. No elastic anomaly was observed in the non-superconducting Dy-1113. The anomaly observed in the superconducting sample is attributed to structural phase transition caused by oxygen orderings.     

AC-Conductivity and proton transport number of BaZr0.90Al0.10O3-δ

AC-conductivity measurements of BaZr_0.90Al_0.10O_3−δ (where δ describes the number of oxygen ion vacancies per unit cell) in wet and dry N₂ have been carried out over the temperature range from 400 to 900 °C. Both atmospheres showed the usual Arrhenius behavior of BaZr_0.90Al_0.10O_2.95. The proton transport number,t _H, was also determined from the conductivity measurements of BaZr_0.90Al_0.10O_2.95 in wet and dry N₂ and takes up values of 0.97 and 0.78 in the temperature range 400 – 900 °C, respectively.     

The across-plane conductivity and microstructure of SrZr0.95Y0.05O3 − δ thin films

The across-plane electrical conductivity of the proton-conducting SrZr_0.95Y_0.05O_3???δ thin films fabricated by chemical solution deposition on single-crystalline ZrO₂ doped by 10 mol% of Y₂O₃ (YSZ) substrates was investigated using impedance spectroscopy. The average grain size of the films was found to increase considerably with thermal treatment. This change in grain size has a strong effect on the electrical behavior of films. Our results show that the electrochemical performance of the cell is strongly affected by the potential difference at the film/substrate interface. Coarse-grain film microstructure was proved to be preferable for the reduction of both the film resistance and interfacial barrier.     

Anisotropic optical properties of single-crystal GdBa2Cu3O7−δ

The optical spectrum of reduced-T _c GdBa₂Cu₃O_7– has been measured for polarizations parallel and perpendicular to theab plane. The sample was an oxygen-deficient single crystal with a large face containing thec axis. The polarized reflectance from this face was measured from 20–300 K in the spectral region from 30–3000 cm^–1, with 300 K data to 30000 cm^–1. Kramers-Kronig analysis was used to determine the spectral dependence of theab and thec components of the dielectric tensor. The optical properties are strongly anisotropic. Theab-plane response resembles that of other reduced-T _c materials whereas thec axis, in contrast, shows only the presence of several phonons. There is a complete absence of charge carrier response alongc aboveand belowT _c. This observation allows us to set an upper limit to the free-carrier spectral weight for transport perpendicular to the CuO₂ planes.Permanent address: Institute of Physics, CSAV, Prague, Czechoslovakia     

Influence of Pr dopant on the dielectric properties and Curie temperatures of Ba1−3x Pr2x Ti0.95Sn0.05O3 (0.01≤x≤0.05) ceramics

Three perovskite-structured ceramic phases Ba_1?3x Pr_2x Ti_0.95Sn_0.05O₃ (BPTS-x) with x=0.01, 0.03, and 0.05 have been synthesized by solid-state reaction method. Obtained BPTS-x ceramics were investigated by X-ray diffraction and dielectric properties measurements. Analysis of all the ceramic samples using X-ray diffraction method at room temperature and its Rietveld refinement inferred rhombohedric structure with the space group $R\bar{3}c$ . The temperature variation of real permittivity gives evidence of the ferroelectric phase transition and of the relaxation behavior. With increasing Pr concentration, the degree of diffuse phase transition was enhanced, and a linear reduction in the transition temperature was produced. The conductivity spectra have been investigated by the Jonscher universal power law (σ(ω)=σ _dc+Aω ^s ) and attributed to hopping conduction mechanism.     

Non-Faradaic electrochemical modification of the catalytic activity of Pt using a CaZr0.9In0.1O3-α proton conductor

The effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) was investigated for the case of C₂H₄ oxidation on a Pt polycrystalline catalyst film also acting as a working electrode in a galvanic cell of the type: $$C_2 H_4 ,O_2 ,CO_2 ,H_2 O,Pt|CaZr_{0.9} In_{0.1} O_{3 - \alpha } |Au,C_2 H_4 , O_2 ,CO_2 ,H_2 O$$ In addition to proton conduction, CaZr_0.9In_0.1O_3-α is known to exhibit oxygen and hole conduction. Proton conduction predominates over the temperature range, 380 to 460 °C, of the present investigation. It was found that negative current application, i.e. proton supply to the Pt catalyst film causes up to 500% reversible enhancement to the rate of C₂H₄ oxidation. The catalytic rate increase is up to 20,000 higher than the rate, -I/F, of proton supply to the catalyst. The observed phenomena are discussed within the framework of previous electrochemical promotion (NEMCA) studies.     

Superconducting and elastic properties of (Dy1−xPrx)BaSrCu3O7−δ

Pr-substituted (Dy_1−xPr_x)BaSrCu₃O_7−δ (x=0.0, 0.1, 0.2, 0.4 and 0.7) has been investigated for its superconducting and elastic properties. Structural transition from orthorhombic to tetragonal symmetry is observed at x=0.1. Temperature-dependent sound velocity was measured using the pulse-echo overlap method. Elastic anomalies in the form of lattice stiffening with decreasing temperature were observed above 200 K. These anomalies were attributed to oxygen vacancy orderings in the Cu(1)O plane and also depended on the configurational state of oxygen orderings which is strongly influenced by Pr-doping.     

Effect of processing on dielectric properties of (0.95)PbZr0.52Ti0.48O3–(0.05)BiFeO3

An effort has been made to synthesize solid solution of a composition with x=0.05 in the system (1?x)PbZr_0.52Ti_0.48O₃–(x)BiFeO₃ by the sol–gel method. XRD patterns of the pure PZT and BFO modified PZT samples have shown single phase formation. The effects of substitution of BFO on dielectric properties of PZT have been studied in the frequency range 10 Hz to 100 kHz and temperature range from RT to 773 K. The density was optimized by sintering the BFO modified PZT samples at different temperatures in four batches, S1, S2, S3 and S4. P–E hysteresis loop measurements for all the samples have shown almost saturated polarization. It has been observed that sample S2, sintered at 950 °C, exhibits superior dielectric properties of the four samples. The occurrence of weak ferromagnetism, observed in the M–H hysteresis loop, indicates coupling between ferroelectricity and magnetism. Impedance analysis has revealed that all the samples, sintered at different temperatures, have a different grain resistance. A large change in ac conductivity around T _c has been observed in all the samples.     

EPR study of the high-TC superconductor YBa2Cu3O7−δ

EPR spectra of superconducting YBa₂Cu₃O_7-δ and insulating Y₂BaCuO₅ have been examined. The intensity of Cu²⁺ ions in YBa₂Cu₃O_7-δ is about 1/3000 of that in Y₂BaCuO₅ at room temperature. Owing to the Meissner effect in the superconducting state, the EPR signal of Cu²⁺ ions in YBa₂Cu₃O_7-δ disappears; moreover the EPR signal of DPPH deposited on the YBa₂Cu₃O_7-δ specimen is shifted. An additional EPR line is found for YBa₂(Cu_2.94Cr_0.06)O_7-δ at temperatures below 113K; this can be related to the phenomenon of superconductivity.     

Effects of heating on the Raman spectra of YBa2Cu3O7−δ

We report effects of heating to the intensities of Raman modes in the spectra of single-crystals embedded in ceramic YBa₂Cu₃O_7– pellets, and compare the results with those from YBa₂Cu₃O_7– thin-films. Heating was done by either increasing the laser-beam power or resistively heating in a heating cell. From the measurements on a single-crystal in z(xx) polarization, we find that the relative intensity of the B_1g mode of the plane oxygens to that of the A_1g mode of apical oxygens decreases strongly as the samples are heated. For a crystal in near x(zz) polarization, the relative intensity of the two modes increases up to certain value. In thin-films, however, no such change was observed even when heated to higher temperatures than the crystals were. Therefore, we interpret that the change in the relative intensity of the two modes of single-crystals is not due to electronic or structural changes nor thermal decomposition in the heated samples. We propose that a single-crystal, when heated, is fractured into many micro-crystals and these micro-crystals thermally fluctuate in orientations. For thin-films, such fluctuation in orientations might be hindered because there are only a few layers of micro-crystals on top of the substrate. Scanning electron micrographs (SEM) of the heated part of the samples seem to provide the evidence of the micro-crystals.     

Influence of Zn concentration on electrical resistance of SmBa2(ZnxCu1−x 3O9−δ

It is known that perovskite type structures (ReBa₂Cu₃O_9–) exhibit superconductivity at temperatures below 90 K /1–3/. The substitution of other ions for Cu is interesting because the Cu-O interactions are probably responsible for the supercoductivity in those systems /4/. In the system Y-Ba-(Ag,Cu)-O Saito found that the gradual decrease of T_c with the increase of Ag concentration is due to the presence of the different phases /5/.In this letter we are reporting the experimental measurements of the electrical resistance of SmBa₂Cu₃O_9– oxygen defect perovskites with Zn substituted for Cu.     

Infrared spectra of superconducting La2−xSrxCuO4 and YBa2Cu3O7−δ

Abstract

Abstract Infrared spectra of La_2?xSr_xCuO₄ and YBa₂Cu₃O_7?δ are discussed, specially with respect to the disappearance of the high-frequency (～650 cm) band of the superconducting compositions at 300K. Some of the bands persist at 300K eventhough the materials are fairly conducting. YBa₂Cu₃O_7?δ does not show evidence in the far IR spectrum for the presence of an optical gap.     

Growth of Ba2−x Sr x NaNb5O15 thin film on La0.05Sr0.95TiO3 substrate by pulsed laser deposition

Ba_2−x Sr _x NaNb₅O₁₅ thin films were prepared on La_0.05Sr_0.95TiO₃ substrates by pulsed laser deposition. The structural and ferroelectric properties of the thin films depended on substrate temperature (T _sub) and Sr concentration. When T _sub was fixed at 700 °C, the Ba_2−x Sr _x NaNb₅O₁₅ (x = 0, 0.6, 1.0, and 1.4) thin films exhibited a high c-axis orientation. The thin films consisted of well-developed grains and exhibited a smooth surface. The c-axis-oriented Ba_0.6Sr_1.4NaNb₅O₁₅ thin film with the lowest Curie temperature also exhibited a high c-axis orientation and a P-E hysteresis loop with a high ferroelectricity at T _sub 650 °C. Thus, its remanent polarization (P _r) and coercive field (E _c) were 2P _r 24.9 μC/cm² and 2E _c 107 kV/cm, respectively. These values indicate that Ba_2−x Sr _x NaNb₅O₁₅ has ferroelectricity in the thin film form.     

Phase Structures of （K0.48Na0.52）0.945Li0.055Sb0.05Nb0.95O3 Piezoceramics

The phase structures of lead-free （K0.48Na0.52）0.945Li0.055Sb0.05Nb0.95O3 piezoceramics are studied based on the measurements of ferroelectric and dielectric properties as well as the analyses of x-ray diffraction pattern and energy dispersive spectroscopy. The poled samples exhibit orthorhombic structure whereas the surface and interior for unpoled samples exhibit tetragonal and tetragonal-orthorhombic coexistent structures, respectively. These results are in agreement with the relative permittivity-temperature curves and demonstrate that phase transitions can be induced by Na volatilization and poling process. The remnant polarization Pr measured at 20°C increases continuously with the increase of electric field in the range of 2000-4000V/mm. This indicates that the polymorphic structure is more beneficial to the rotation or reorientation of dipoles than either the orthorhombic or the tetragonal structure. The randomly oriented domains may be the essential reason for the continuous rotation or reorientation and not good thermal stability.