超导Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x复合氧化物摩擦磨损性能

为适应20℃～-200℃ 温度的适用范围,采用固相法制备了Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x超导材料,用摩擦磨损试验机测试了Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x从液氮温度至室温的摩擦学性能。结果表明 : 在室温 20℃下,Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x与对偶件轴承钢盘对摩时,摩擦系数约为0.35,当温度降到超导转变温度以下时(液氮温度-170℃)摩擦系数大幅度降低,Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x超导态摩擦系数为正常态值的一半,实验证明了电子激励对摩擦能量耗散的作用。为改善室温下Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x摩擦学性能,掺杂不同质量分数 Ag作为润滑组元,制备了Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x超导固体润滑复合材料,取得良好耐磨减摩效果。Ag掺杂不影响Ag/Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x复合材料的超导性,在正常载荷和滑动速度下10 wt%Ag/ Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x复合材料摩擦系数为0.2~0.3,磨损率为4.57×10-4 mm3·(N·m)-1。     

Thermoelectric Power of Deoxygenated Bi1.6Pb0.4Sr2Ca2Cu3O10 + δ Sintered Superconducting Pellets

The thermal variation of the electrical resistivity and thermoelectric power of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_{10 +} pellets subjected to various degrees of deoxygenation is reported. The temperature dependence of the electrical resistivities of deoxygenated samples displays gradual transformation from metallic-like to semiconductor-like features in the normal state. All the samples however, show superconducting transition, but increasing deoxygenation depresses T _C0 from 102 to 45 K. Gross features of the temperature variation of thermoelectric power observed in properly oxygenated (Bi, Pb)-2223 cuprates are retained in all the deoxygenated samples. Our results on electrical resistivity and thermoelectric power in the normal state have been found to be consistent with a two-band model.     

The Effect of Silver Substitution in Bi1.7Pb0.3Sr2Ca2?xAgxCu3Oy

The effect of Ag substitution on the properties of high-temperature superconductor Bi_1.7Pb_0.3Sr₂Ca_2−x Ag _x Cu₃O _y system have been investigated. The electrical and structural properties of the samples, prepared by the conventional solid-state reaction method, have been characterized by X-ray diffraction (XRD), electrical resistance and scanning electron microscopy (SEM) studies. XRD analysis reveals a multiphase structure of the samples, whereas SEM micrographs indicate some morphological changes induced by silver addition. It was found that an increase of the amount of Ag₂O addition leads to an enhancement of the critical temperature and the percentage of Bi-2223 phase in the phase mixture.     

A Study of the Magnetic Properties of?Bi1.64?xPb0.36CdxSr2Ca2Cu3Oy Superconductor

The flux pinning energy and magnetic properties of Bi_1.64−x Pb_0.36Cd _x Sr₂Ca₂Cu₃O _y (BPCSCCO) with x=0.0, 0.02, 0.04 and 0.06 were studied. A series of Bi-2223 superconductor samples with a nominal composition of BPCSCCO was synthesized and the effect of Cd substitution for Bi was investigated. As a result, Cd addition has been found to improve the superconducting properties of the Bi-Pb-Sr-Ca-Cu-O system. The effects of the annealing time and the amount of Cd doping on the structure, AC magnetic susceptibility, ρ–T curves and flux pinning energy were investigated. Also, for all samples the relation between the current and voltage in the mixed state was found to follow the model relationship V=α I ^β . The maximum value of β is 22.30, which is obtained for the sample with an annealing time of 270 h and a Cd content of 0.04.     

Study on the Physical and Electrical Properties of Bi2 ? δZnδSr2Ca2Cu3O10 + y Glass-Ceramic Superconductors

We have fabricated a series of glass-ceramic (Bi_{2 –} Zn) Sr₂Ca₂Cu₃O_{10 + y} , where = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, and investigated the effect of Zn ions on the glass formation, crystallization, thermal, electrical, and on the magnetic properties of the BSCCO-2223 superconductor system. The structural symmetry was found to be tetragonal in all the substitution levels. The best electrical performance was obtained from the = 0 sample, the T _c and T _zero was obtained at 110 K and 107 K, respectively. The J _c values of the samples were determined using the magnetization hysteresis and Bean's model. The crystallization kinetics were investigated using nonisothermal models of Augis–Bennett. The calculated activation energy, E _a, of the system was found to be in the range of 258–336 kJ/mol.     

Transport properties of oxygen-deficient YBa2Cu3O7?x thin films

We report on measurements of the in-plane resistivity and Hall coefficientR _H (Bc) of various oxygen-deficient epitaxial films of YBa₂Cu₃O_7–x in the normal state. The superconducting transition temperaturesT _c of the samples vary from 14 to 90 K. Both the resistivity and the Hall coefficient exhibit a strong dependence on the oxygen content and the temperature. Asx increases,T _c decreases continuously, while andR _H gradually increase in magnitude. Furthermore, also the characteristic linear dependences ofT andR _H T ^–1 of the highly doped compounds changes to a nonlinear behavior for the samples withT _c lower than 60 K. The unusual doping and temperature dependence ofR _H will be compared to the predictions of our calculations, based on a two-dimensional tight-binding model using the relaxation-time approximation. The model considers also the next-nearest-neighbor hopping, which strongly influences the predicted Hall coefficient. Additionally, the cotangent of the Hall angle cot( _H ) is discussed in the framework of the two-dimensional Luttinger liquid theory.We gratefully acknowledge financial support from the Bundesministerium fiir Forschung und Technologic.     

The Influence of Lithium Halides on the Superconducting Properties of YB2Cu3O7?x

The effects of addition to YBa₂Cu₃O_7–x of lithium halides (YBa₂Cu₃O_7–x (LiF) _y , and YBa₂Cu₃O_7–x (LiCl) _y ) on the structural, electric, magnetic, and transport properties are analyzed. Both structural and superconducting properties depend weakly on the lithium content up to y= 0.10. The critical temperature keeps on a value well above 91 K for a small amount of lithium halide (reaching 93.48K. for y= 0.02 in YBa₂Cu₃O_7–x (LiF) _y and 91.30 K in YBa₂Cu₃O_7–x (LiCl) _y ), but for higher concentration of Li it rapidly decreases (81.68K for y= 0.20). The same behavior is exhibited in the lower intragranular critical field. The intragranular critical current density depends on the magnetic field as a power law:j _cB ^–, with a lithium-concentration-dependent . The voltage–current characteristics follow a law typical for granular superconductors, V(I–I _c(B,T)) ^n(B,T). The dependence of the intergranular critical current, I _c, and of the exponent, n, on temperature, magnetic field, and concentration is analyzed.     

Electrical conductivity and thermal stability of (1 ? x )CsH2PO4/ x SiP y O z ( x = 0.2–0.7) composites

The physicochemical properties of (1 − x)CsH₂PO₄/xSiP _y O _z (x = 0.2–0.7) composites containing fine-particle silicon phosphates as heterogeneous additives have been studied at different humidities. The introduction of silicon phosphates suppresses the superionic phase transition of CsH₂PO₄ and increases the low-temperature conductivity of the materials, which depends significantly on humidity. The CsH₂PO₄-SiP _y O _z materials offer high conductivity (∼3 × 10⁻³ to 10⁻² S/cm at ∼110–230°C) at low water vapor pressures (3 mol % H₂O). Amorphization of the CsH₂PO₄ in the composites markedly changes its thermodynamic properties. The effect of long-term isothermal holding (210°C, 3 mol % H₂O) on the conductivity of the composites has been studied. Original Russian Text ? V.G. Ponomareva, E.S. Shutova, G.V. Lavrova, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 9, pp. 1131–1136.     

Effect of Nano-Sized ZnO on the Physical Properties of (Cu0.5Tl0.25Pb0.25)Ba2Ca2Cu3O10?δ

High-temperature superconductor phase of (Cu_0.5Tl_0.25Pb_0.25)-1223 was synthesized by solid-state reaction technique and characterized using X-ray powder diffraction (XRD). XRD analysis revealed that the prepared sample was nearly monophase and exhibited tetragonal structure with space group P4/mmm. Nano-zinc-oxide, prepared by Co-precipitation method, was added to the sample. ZnO-concentrations y varied from 0.0 to 2.0 wt.% of the sample’s mass. The prepared samples were investigated through XRD, scanning electron microscope (SEM), energy dispersive X-ray (EDX), particle size analyzer (PSA), differential scanning calorimeter (DSC), electrical resistivity and transport critical current density measurement. X-ray data analysis showed that the nano-Zn addition does not affect the tetragonal structure of (Cu_0.5Tl_0.25Pb_0.25)-1223 phase, whereas the lattice parameters showed an insignificant variation. The results of the superconducting transition temperature, the transport critical current density and melting point of the prepared samples were found to depend on nano-ZnO concentrations.     

Characterization of Submicron Sized Josephson Junction Fabricated in a Bi2Sr2Ca2Cu3O10+δ (Bi-2223) Single Crystal Whisker

To study the detailed characteristics of a nano-periodic Josephson junction array in a Bi₂Sr₂Ca₂Cu₃O_10+δ (Bi-2223) single crystal whisker without shunted grain boundaries, we fabricate a submicron stack with an area of 0.5 μm×0.5 μm and height of approximately 200 nm using a focused ion beam (FIB) etching technique. The stack has several hundreds of elementary Josephson junctions along the c-axis. We fabricate the stack by rotation and tilt of the sample stage in the FIB. The current–voltage (I–V) characteristics give a well-defined superconducting gap (V _g) and we notice suppression of the critical current in submicron junction with respect to big sized junction. We believe that the suppression of critical current in submicron junction is due to the normal resistance of the junction which belongs to the quantum resistance range.     

Effect of heat treatment in sulfur and mercury vapors on the magnetic susceptibility of Hg1 ? x Mn x Te1 ? y S y crystals

We have studied the effect of heat treatment in mercury and sulfur vapors on the magnetic susceptibility of Hg_{1 − x} Mn _x Te_{1 − y} S _y crystals. Measurements were performed by the Faraday method in the temperature range 77–300 K at H= 318 kA/m before and after heat treatments. The results demonstrate that the behavior of the magnetic susceptibility can be understood in terms of Mn-S-Mn-S, Mn-Te-Mn-Te, and (mixed) Mn-Te-Mn-S clusters of different sizes with indirect antiferromagnetic exchange interaction between the Mn atoms through the chalcogen atoms. Heat treatment in sulfur and mercury vapors leads to the formation of new clusters or changes (increases or decreases) the size of already existing clusters. Original Russian Text ? P.D. Maryanchuk, E.V. Maistruk, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 5, pp. 549–554.     

Potassium ion conducting K2 ? 2 x Fe2 ? x P x O4 solid electrolytes

Potassium ion conducting solid electrolytes based on potassium monoferrite have been prepared by substituting pentavalent phosphorus cations for Fe³⁺. The highest conductivity of K_{2 − 2x} Fe_{2 − x} P _x O₄ is achieved in the range x = 0.05−0.10: 7.1 × 10⁻³ S/cm at 300°C and 1.6 × 10⁻¹ S/cm at 700°C. The rise in the conductivity of KFeO₂ upon phosphorus doping is due to the formation of potassium vacancies. Original Russian Text ? E.I. Burmakin, G.Sh. Shekhtman, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 8, pp. 995–998.     

Sintering time and properties of YBa2Cu3O～7 superconducting ceramics

The effect of annealing duration in oxygen flow on the superconducting characteristics of YBa₂Cu₃O₇ bulk ceramics was investigated by structural, electrical, magnetic, and electronic microscopy investigations. The long-time annealing is deleterious for the superconductivity in YBa₂Cu₃O₇ ceramics. The optimum time interval for annealing is from 20 to 70 h at 950°C, and within this range the maximum value ofT _c is obtained.     

Cd-Doped Cu0.5Tl0.5Ba2Ca2Cu3?yCdyO10?δ (y=0,0.5,1.0,1.5,2.0) Superconductors

Superconducting properties of cadmium doped Cu_0.5Tl_0.5Ba₂Ca₂Cu_3−y Cd _y O_10−δ (y=0,0.5,1.0,1.5,2.0) samples have been studied using X-ray diffraction, resistivity, ac-susceptibility and FTIR absorption measurements. In X-ray diffraction studies these samples have shown to have tetragonal structure. The zero resistivity critical temperature and magnitude of diamagnetism are suppressed with the increased incorporation of Cd in the final compound. A change in the shape of FTIR absorption spectra, after doping, has shown the incorporation of Cd in the unit cell. A systematic hardening of the apical oxygen modes and softening of the CuO₂ planar modes of vibration with increased Cd doping have shown that it is incorporated in the unit cell of Cu_0.5Tl_0.5Ba₂Ca₂Cu_3−y Cd _y O_10−δ (y=0,0.5,1.0,1.5,2.0) superconductors. The FTIR absorption measurements of these samples have shown that hardening of the apical oxygen modes of types Cu(1)–O(2)–Tl and Cu(1)–O(2)–Cu(2)/Cd _y (y=0,0.5,1.0,1.5,2.0) increases with the increase of Cd doping in the samples. A softening of the CuO₂ planar oxygen mode Cu(2)–O–Cu(2) is also observed with the increased Cd doping in the final compound. It is most likely that hardening of the apical oxygen modes and the softening of the planar modes of vibration are associated damped harmonic oscillations produced by heavier Cd atoms in the CuO₂ planes, which suppress the phonon population from a desired level, reducing the magnitude of superconductivity in the final compound.     

Dielectric, ferromagnetic and ferroelectric properties of the (1 ? x)Ba0.8Sr0.2TiO3–xCoFe2O4 multiferroic particulate ceramic composites

The (1 − x)Ba_0.8Sr_0.2TiO₃–xCoFe₂O₄ ceramic composites (x = 0–1) were prepared by standard solid state reaction method. X-ray diffraction and SEM indicate the Ba_0.8Sr_0.2TiO₃ (BST) phase and CoFe₂O₄ (CFO) phase coexist in the composites. The dielectric constant and dielectric loss for the composites were studied as a function of frequency (40 Hz–1 MHz) and temperature (30–600 °C). Magnetic and ferroelectric tests show that the ceramic composites display ferromagnetic and ferroelectric properties simultaneously. The saturated polarization of the composites decrease with ferrite concentration increasing, while the remnant polarization of the composites increase with increasing ferrite concentration. The enhanced ferroelectricity of composites may be attributed to space charge contribution in the composites.     

Investigation of the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. II: The series LaMn0.25?xCo0.75?xCu2xO3?δ and LaMn0.75?xCo0.25?xCu2xO3?δ

This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ and LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO₃–LaCoO₃–“LaCuO₃”. The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich series (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ), the Mn-rich series (LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 °C. The Co-rich series showed higher thermal expansion coefficients (α_max = 19.6 × 10⁻⁶ K⁻¹) and electrical conductivity (σ_max = 730 S/cm at 800 °C) than the Mn-rich series (α_max = 10.6 × 10⁻⁶ K⁻¹, σ_max = 94 S/cm at 800 °C). Irregularities in the thermal expansion curves indicated phase transitions at 150–350 °C for the Mn-rich series, while partial melting occurred at 980–1000 °C for the Co-rich series with x > 0.15. I. Arul Raj—on leave from Central Electrochemical Research Institute, Karaikudi, 630006 India.     

Dependence of microwave surface resistance on the structure of laser-deposited YBa2Cu3O7?x thin films

The effect of the structure YBa₂Cu₃O_7-x superconducting thin films on microwave surface resistance was investigated. The electon channeling patterns (ECPs) and X-ray experimental results showed that the microwave surface resistanceR _s is strongly correlated with the perfection of the thin films. The films were deposited on LaAlO₃(100) and YSZ(100) substrates. For thin film withR _s of 280, the crystallinity of the thin film shown byw-scanning and-scanning was excellent and the ECPs were very sharp. For thin film with highR _s of 98 m, only bands from the major zone were visible in the ECPs, which suggested poor crystallinity of the film. From this investigation it was shown that the more perfect the thin films, the lower theR _s.     

Elastic and inelastic properties of (Co0.45Fe0.45Zr0.1) x (Al2O3)1 ? x nanocomposites

The elastic (Young’s modulus) and inelastic (internal friction) properties of amorphous (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} nanocomposites with various relative contents of the metallic and dielectric phases have been studied. In the region of low temperatures, the composites exhibit a peak of the internal friction (at ∼240 K), the intensity of which increases with the content of the metallic phase. For compositions above the percolation threshold, the temperature dependence of the internal friction exhibits exponential growth above 300°C, which is related to the migration of vacancy-like defects in the amorphous structure of the metallic phase.     

Enhancement of the Current Density J C for Bi2Sr2CaCu2O8 by?Means of Carbon and NbSe2 Nanotubes

Three polycrystalline Bi₂Sr₂CaCu₂O₈, Bi₂Sr₂CaCu₂O₈ with carbon nanotubes, Bi₂Sr₂CaCu₂O₈ with NbSe₂ nanotubes were synthesized by solid state reaction method and studied by scanning electron microscopy, X-ray diffraction, magnetization measurements, and high resolution transmission electron microscopy. The critical temperature T _C for the three compounds was about 85 K. There is an enhancement in the critical current density, J _C for samples with carbon and NbSe₂ nanotubes as compared with pure Bi₂Sr₂CaCu₂O₈. The enhancement provides evidence that wetting exists for the two doped samples investigated.      

The Effects of Substitution of Sn for Cu in Bi1.75Pb0.25Sr2CaCu2.3?xSnxSnxOy

The influence of Sn doping on superconductivity in the Bi-based 2212 phase is studied in this paper. For the samples R–T relations and magnetic hysteresis loops were measured. X-ray powder diffraction analysis was also performed. For Bi_1.75Pb_0.25Sr₂CaCu_2.3–x Sn _x O _y , the experimental results show that by adding the proper amount of Sn the superconductivity of the samples can be improved. As x = 0.15, the critical temperature T _c, the critical current density J _c, and the magnetic pinning force density F reach a maximum. At T = 11 K, the critical state parameters H _c1, H _c2, , , and are calculated and compared with the results reported by other researchers. The experimental results also show that the Sn doping is able to speed up the growth of the 2223 phase. In brief, Sn doping is an effective way of improving the superconductivity in Bi-based superconductors.