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1.
Energy dispersive X-ray spectroscopy (EDX) and electron diffraction and high-resolution electron microscopy are used to study the composition and structure of anode and cathode deposits formed during the high temperature (950°C) electrolysis of the Y-Ba-Cu-O system and low temperature (450°C) electrolysis of the Y-Ba-Cu-K-O system. It is found for the first time that an oxide with the YBa2Cu3O y structure (123 phase) is synthesized during the high temperature electrolysis of Y0.02Ba0.30Cu0.70O y and Y0.02Ba0.25Cu0.75O y melts. The 123 phase is not synthesized during low temperature electrolysis, where melts are formed from Y2O3, BaO2, CuO, and KOH. Two new Pt-containing oxides with hexagonal structure are found in the products of high temperature electrolysis.  相似文献   

2.
The cation composition and structure of YBa2Cu3O7 ? δ (YBCO, the 123 phase) oxide samples synthesized at 990°C in air and annealed in oxygen at 450°C are studied via elemental analysis in a transmission electron microscope and high-resolution electron microscopy. The occurrence of cation nonstoichiometry and nanostructured inhomogeneity of the 123 phase in tetragonal and orthorhombic (superconducting) structures is confirmed. The nanostructured inhomogeneity of the 123 phase is attributed to the presence of nanocrystallites (2–5 nm) of oxides with different cation compositions belonging to the Y n Ba m Cu m + n O y series.  相似文献   

3.
The phase composition of Y z Ba5Cu7O y (1) and Y z Ba3Cu5O y (2) samples with a variable percentage of yttrium up to the stoichiometric composition of the Y n Ba m Cu m + n O y series is investigated by X-ray phase and elemental analyses, electron diffraction, and high resolution imaging in a transmission electron microscope at a temperature of 930°C in the crystallization field of a matrix oxide (Ba: Cu) of 5: 6 composition on the phase diagram of the BaO-CuO x system at P(O2) = 21 kPa. The substantial effect of yttrium oxide’s presence on the phase composition of both objects is found, providing evidence of a complex ionic equilibrium within the melt. The fine-domain oxide structure of the YBa2Cu3O6 tetragonal form, which is due to the coexistence of oxides of an Y n Ba m Cu m+n O y homologous series of (Y: Ba: Cu) 235, 123, and 257 composition is revealed. The domain size for these phases is 20–50 ?. The domains are joined coherently along axis c.  相似文献   

4.
The phase composition of specimens in the primary crystallization field of the Y n Ba m Cu m + n O y oxide series with compositions of (Y:Ba:Cu) 235, 123, and 257 was investigated by means of X-ray powder diffraction, X-ray microprobe analysis, electron diffraction, and high resolution imaging in a transmission electron microscope. Y n Ba m Cu m + n O y oxides have the YaBa2Cu3O6 tetragonal structure and can be represented in the general form as 123 oxides. It was found that the crystallization field of 123 oxides corresponds to the crystallization fields of the Ba m Cu m + n O y oxide series with the BaCuO2 cubic structure. These crystallization fields are located in the matrix phase diagram of the BaO-CuO x system at P(O2) = 21 kPa in the range of 50–90 mol % CuO and 910–1000°C. The 123 oxides are formed according to an intercalation mechanism with the participation of barium-copper oxide matrices with the composition (Ba: Cu) 3: 5, 2: 3, and 5: 7  相似文献   

5.
Phase relations have been studied in the BaO–CuOx system in the range of 42.0–83.0 mol.% CuO at P(O2) = 21 kPa (air) by visual polythermal analysis (VPA), powder X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), chemical analysis (CA), and electron diffraction (ED) with simultaneous elemental analysis (EA) in a transmission electron microscope (TEM). The existence of discrete crystallization fields of barium–copper oxides of cation compositions Ba4Cu5Oy, Ba5Cu6Oy, Ba7Cu8Oy, Ba12Cu13Oy, and Ba24Cu25Oy, which have the cubic structure of the BaCuO2 oxide, is revealed in the studied region of the system. The oxides may be represented as members of a BamCum+nOy homologous series. The BaCuO2 oxide does not exist in the subsolidus region and does not have its own crystallization field. The oxygen-deficient oxide BaCuO1.78 of the cation composition (Ba:Cu) 1:1 with the BaCuO2 cubic structure is found in melted samples of the 50.0 mol.% CuO composition quenched at 1020–1060 °С.  相似文献   

6.
Commercial high-T c superconducting tape produced by Superpower Inc. (the U.S.A.) is studied by scanning and transmission electron microscopy. The superconductor structure is shown to consist of a superconducting layer of average composition GdBa1.5Cu2.5–3.0O y coated by a silver layer and buffer layers of LaMnO3, MgO,Y2O3, and Al2O3 deposited on a metallic tape of nickel alloy (Ni-Cr-Mo-Fe-W-Co-Mn). The superconducting layer is formed by the superconducting oxide GdBa2Cu3O y containing lamellar inclusions Gd2O3.  相似文献   

7.
The temperature dependence of the thermoelectric power in samples of Y1−x PrxBa2Cu3Oy (x=0−0.6) is investigated. The principal parameters of the system of charge carriers are determined on the basis of an analysis of this dependence within a narrow-conduction-band model, and their variation with increasing praseodymium content is analyzed. It is found that an increase in x leads to a very weak increase in the electron filling and considerable broadening of the conduction band accompanied by strong localization of the charge carriers. It is concluded on the basis of a comparative analysis of the results obtained and data for the YBa2Cu3Oy system in the case of aliovalent substitutions in the barium and copper sites that the valence of praseodymium in Y1−x PrxBa2Cu3Oy is very close to 3+. It is shown that there is a universal correlation between the effective width of the conduction band and the critical temperature following various cation substitutions in the Y-Ba-Cu-O system. It is concluded that the main reason for suppression of the superconducting properties of Y1−x PrxBa2Cu3Oy is the strong modification of the band spectrum caused by praseodymium. Fiz. Tverd. Tela (St. Petersburg) 39, 1520–1525 (September 1997)  相似文献   

8.
We report the grain-orientation effects under a modulated rotation magnetic field for Y-based cuprate superconductors and LaFeAsO (La1111). Tri-axial orientation has been successfully achieved only for orthorhombic Y2Ba4Cu7Oy and YBa2Cu4O8 powders without a twin microstructure, while separation of three crystallographic axes could not be observed in twinned YBa2Cu3Oy (Y123) and tetragonal La1111 powders. The morphology of grains, in addition to the symmetry of crystal structures, seriously affects the degrees of tri-axial orientation, which means that the control of twin microstructures is required for the tri-axial magnetic orientation in Y123.  相似文献   

9.
A top-seeded melt-growth (TSMG) process is widely used to fabricate single domain YBa2Cu3Oy (Y–Ba–Cu–O) bulk superconductors. Pores are often found in the TSMG-processed Y–Ba–Cu–O samples due to the oxygen gas evolution during the molten stage. Recently developed liquid infiltration growth (LIG) process is known to be effective in suppressing the pore evolution and in refining the size of Y2BaCuO5 (Y211) particles dispersed in YBa2Cu3Oy matrix. The LIG process utilizes the liquid (Ba3Cu5O8) infiltration into a pre- sintered Y211 contact and slow cooling through a peritectic temperature. In this study, we fabricated bulk Y–Ba–Cu–O superconductors by the LIG process combined with top-seeding with SmBa2Cu3Oy seed and confirmed that a single-domain bulk can be produced. Trapped field measurements however showed that some distortion in the field distribution was observed in the region near the seed crystal, which was attributed to Y211 density and its relatively large size.  相似文献   

10.
The temperature dependence of the Nernst-Ettingshausen coefficient Q(T) in the normal phase of doped HTSCs of the yttrium system was studied. The main features characterizing the behavior of this coefficient were revealed, and the character and mechanism of the effect that various nonisovalent substituents exert on the Q(T) dependence were analyzed. It is shown that the narrow-band model permits one not only to describe all the specific features observed in the Q(T) curves but also to perform a simultaneous quantitative analysis of the temperature dependences of four kinetic coefficients (the electrical resistivity and the Seebeck, Hall, and Nernst-Ettingshausen coefficients) with the use of a common set of model parameters characterizing the band structure and carrier system in the normal phase of an HTSC. This approach was employed to determine the carrier mobilities and the asymmetry of the dispersion curve in the systems studied (YBa2Cu3Oy, y = 6.37–6.91; YBa2Cu3?xCoxOy, x = 0–0.3; Y1?xCaxBa2Cu3Oy, x = 0–0.25; Y1?xCaxBa2?xLaxCu3Oy, x = 0–0.5) and to analyze the effect of the substitutions involved on the variation of these parameters.  相似文献   

11.
To suppress the samarium diffusion from a SmBa2Cu3O7?y (Sm123) seed into an YBa2Cu3O7?y (Y123) compact during a top seeded melt growth (TSMG) process, Y211 buffer disks of various thicknesses (t) were inserted at the seed/compact interface. The effectiveness of the Y211 buffer insert on the suppression of samarium diffusion was estimated from the susceptibility curve and composition analysis for the three top surface regions (region just below the seed/buffer, intermediate region between the buffer and compact edge and compact edge). The difference in the superconducting temperature (Tc) and the superconducting transition width (ΔT) in the three regions was large, when no buffer or thin buffers (t is smaller than 1 mm) were used. As a buffer disk of an appropriate thickness was inserted into the seed/compact interface, the difference in Tc and ΔT in the three regions was much reduced. The composition analysis across the seed/buffer/compact region clearly revealed that the Tc decrease was caused by the samarium diffusion from a seed, which led to the formation of Y1?xSmxBa2Cu3O7?y in the Y123 compact region. The buffer insert technique was demonstrated to insure the uniform superconducting properties of the top surface of TSMG processed Y123 superconductors.  相似文献   

12.
To understand the effect of Y2BaCuO5 (Y211)/YBa2Cu3O7?y (Y123) interfaces on the oxygen diffusion in single grain YBa2Cu3O7?y superconductors, single grain Y123 superconductors with 0.05 and 0.3 moles of Y2O3 additions were fabricated by a top-seeded melt growth (TSMG) process. Y123 compacts with Y2O3 additions were subjected to melt growth heating cycles with a cooling rate of 1 °C/h through a peritectic temperature (1015 °C) and then annealed at 450 °C for 200 h in flowing oxygen. The superconducting temperature (Tc) and critical current density (Jc) were estimated for the three different regions (top surface (s), intermediate (i) and center (c)) of samples. The amount of Y211/Y123 interface area in single grain Y123 superconductors was successfully controlled by Y2O3 additions. The Tc values of s regions were higher than those of i and c regions, which indicates the presence of more oxygen at the sample surfaces. In addition, the Tc values of i and c regions of the Y123 sample with 0.3 mole Y2O3 addition were higher than those of the same regions of the Y123 sample with 0.05 mole Y2O3 addition due to the promoted oxygen diffusion through Y211/Y123 interfaces and other related defects. In spite of the promoted oxygen diffusion by Y2O3 addition, the large Tc difference among the regions still existed, which suggests sluggish oxygen diffusion into single Y123 grains.  相似文献   

13.
The orthorhombic structure of Ba2Cu2.89O6−y (sp. gr. Pccm, a=13.065(15), b=20.654(21) and c=11.431(8) Å) contains two nonintersecting symmetrically equivalent sets of parallel CuO2-chains running along [110] and [1̄10] directions. Along the c-axis the Cu–O sheets are separated by identical layers of Ba-atoms. The Cu–O chains are distorted within the xy plane producing zigzag. Three of 14 positions of copper atoms were found to be partly vacant that caused the significant shifts of the neighbouring Ba atoms in the plane. The determined structure of Ba2Cu2.89O6−y is compared to that of the monoclinic Ba2Cu3O6 modification, of another infinite-chain compound Sr0.73CuO2, and to one of the substructures of ladder compounds (Sr,Ca)14Cu24O41+y. The superconductivity in Ba2Cu2.89O6−y is associated with the CuO2-chains consisting of CuO4-squares sharing edges. The attention is paid to the coincidence of the temperatures of the superconducting transitions in Ba2Cu2.89O6−y and in ladder compound with the temperature of the sharp magnetic transition in another infinite-chain compound Sr0.73CuO2.  相似文献   

14.
Superconductivity around 90K is observed in mixed and single phase system of LnBaCuO (Ln = Y, Ho, Er). Resistivity, X-ray powder diffraction and AC susceptibility measurements were carried out on samples of the mixed phase systems Ln2−xBaxCuO4−y (Ln = Ho, Er), Y1.2Ba0.8Cu1+xO4+x−y(0<x<5) and single phase system Ba2LnCu3O7 (Ln = Y, Ho, Er). Ln2−xBaxCuO4−y consists of Ba2LnCu3O7, BaCuLn2O5, Cu2Ln2O5 and starting materials and shows a small diamagnetic signal below Tc in the temperature dependent AC susceptibility. Y1.2Ba0.8Cu1+xO4+x−y is a mixture of Ba2YCu3O7, BaCuY2O5 and CuO and also indicates a small diamagnetic signal at 92K. Interesting resistivity anomalies occur in the Y1.2Ba0.8Cu4O7−y and Ho0.8Ba1.2CuO4−y composites including large drops in the resistivity at ∼220 and ∼120K, respectively. The pure compounds, Ba2LnCu3O7 (Ln = Y, Ho, Er) show sharp resistive superconducting transitions and bulk Meissner effects of 90%.  相似文献   

15.
《Solid State Ionics》1999,116(1-2):139-143
We report the synthesis of YBa2Cu3O7−δ (Y-123 phase)-single crystals, through a different path to the traditional one – which involves Y2BaCuO5 (Y-211 phase) as a precursor –. In our case, at 970°C a Pt compound appears: Y2Ba3Cu2PtO10 which dissolves in the melt when heated at 1100°C allowing the growth of Y-123 phase. Large single crystals of Y-123 phase obtained through the route developed in this study showed good superconducting properties with a transition temperature onset at about 85 K; this transition temperature is shifted towards higher temperatures through oxygenation processes that are favoured by their dimensions.  相似文献   

16.
The ceramic sample of Y0.85Ca0.15Ba2Cu3O7−δ was prepared by standard solid-state reaction method, and samples with different oxygen concentration were obtained by quenching from high temperature. The internal friction was measured using the vibrating reed method from liquid-nitrogen temperature to room temperature at kilohertz frequency. An internal friction peak was observed around 250 K in Y0.85Ca0.15Ba2Cu3O7−δ quenched from 1023 K. The peak is related to the one observed around 220 K (labeled as P3 peak) in undoped YBa2Cu3O7−δ (Y123). This result shows the dependence of P3 peak on carriers density and P3 peak has a strong correlation to the abnormal behavior of Y123 in the underdoped range. The variation of two low temperature thermal activated relaxation peaks (P1 and P2) on oxygen content were also investigated. And consistent explanations were given based on all recent researches.  相似文献   

17.
The effect of calcium doping on the superconducting properties of top seeded melt growth (TSMG) processed Y1.5Ba2?xCaxCu3Oy superconductors was studied in terms of calcium content (Xca). YBa2?xCaxCu3O7?δ (Xca = 0, 0.005, 0.01, 0.02, 0.04, 0.1, 0.3) powders were synthesized by the powder calcination method. YBa2?xCaxCu3O7?δ powders were mixed with 0.25 mole Y2O3 powder and 1 wt.% CeO2 as Y2BaCuO5 (Y211) refiner, and finally made into Y1.5Ba2?xCaxCu3Oy (Y1.5) + 1 wt.% CeO2 composition. The single Y123 growth on the top surface was observed up to Xca = 0.1, while the multiple Y123 growth was observed at Xca ? 0.1. The superconducting transition temperature (Tc) and critical current density (Jc) of TSMG processed Y1.5 samples were inversely proportional to Xca. The Y211 size increased with increasing Xca due to the enhancement of Y211 coarsening by calcium doping. No Y211 refining effect by CeO2 was observed in the calcium doped samples. The Tc and Jc decrease by calcium doping are likely to be due to the calcium incorporation with the Y123 lattice and formation of coarse Y211 particles.  相似文献   

18.
Abstract—The interaction of YBa2Cu3Oy (123) with water vapor at temperatures T ≤ 150° has been studied. It has been shown that, with an increase in temperature, the mechanism of its interaction with water changes. Near room temperature, the main process is hydrolytic decomposition. At T ~ 100°C, the absorption of water is significantly reduced, because the role of hydrolysis becomes less important and water penetrates the structure weakly and is incorporated into oxygen vacancies mainly in the form of OH–-groups, which leads to the transition of YBa2Cu3Oy from the tetragonal to orthorhombic phase. With an increase in temperature to 150°C, the absorption of water increases again. In this case, the main mechanism is the penetration of water to the 123 structure, which leads to splitting of Cu–O chains and a phase transition from the 123 to pseudo-124 structure. The role of different mechanisms of interaction with water essentially depends on the oxygen content in the 123 structure. At a low oxygen index (y = 6.3), the role of hydrolysis is more important, and, at y ≥ 6.5, the incorporation of water into the structure prevails. It has been revealed that, at T = 150°C, after absorption of water, YBa2Cu3O6.96 becomes a proton conductor.  相似文献   

19.
The normal-state transport properties and the critical temperature, Tc, for three series of Y1?xCaxBa2Cu2.8Zn0.2Oy (x = 0–0.2) samples with different oxygen content have been investigated and discussed in comparison with results for other calcium-doped YBa2Cu3Oy. We have observed the calcium doping to restore the superconductivity in the YBa2Cu3Oy system even in case of the preliminary Tc suppression by the direct destruction of the CuO2 planes due to a preliminary doping by zinc. The Tc value rises strongly with increasing calcium content and this rise becomes faster for the oxygen-reduced series. Based on a narrow-band model, the parameters of the band spectrum structure and the charge-carrier system in the normal state were determined from the analysis of the thermopower temperature dependences in order to reveal the mechanism of the Tc rise under the Ca influence. It is shown that the Tc increase in Y1?xCaxBa2Cu2.8Zn0.2Oy is related to the direct Ca ions effect. The mechanism of the calcium influence on the Tc value is discussed with respect to the Ca-induced conduction band modification. The calcium doping in Y1?xCaxBa2Cu2.8Zn0.2Oy is shown to give a noticeable contribution to the density-of-states function leading to a strong rise in its value at the Fermi level that results in a restoration of the superconducting properties.  相似文献   

20.
Mono-domain YBa2Cu3O7?x (Y123) bulk superconductors have been processed using seeded infiltration growth technique (SIG). The combination of melt infiltrated liquid source (Ba3Cu5O8) into the Y2BaCuO5 (Y211) pre-form and the nucleation of Y123 domain from SmBa2Cu3O7 crystal seed has been investigated. The different configurations of SIG process were compared in this study. In addition, the effect of the starting Y211 particles size has been studied. The results reveal that, the Y211 particle size and different configurations strongly influence the properties of the final bulk superconductor sample.  相似文献   

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