共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Kokkaliaris S. N. Gordeev P. A. J. de Groot R. Gagnon L. Taillefer P. F. Henry M. T. Weller 《Physica C: Superconductivity and its Applications》1999,320(3-4):161-166
We have investigated the second magnetization peak in pure YBa2Cu3O7−δ single crystals with various oxygen contents (6.91<7−δ<6.97) and degrees of oxygen vacancy ordering, as achieved by low (1 bar) and high (100 bar) oxygen pressure annealing. Although the position of the peak changes drastically with oxygen stoichiometry, no dependence on the distribution of oxygen vacancies has been found for temperatures below 70 K. For T>70 K, however, ordering effects become important as demonstrated by the disappearance of the peak for the high pressure annealed samples. These results suggest that while at low temperatures, pinning of the vortex system by clusters or a more homogeneous distribution of oxygen vacancies is similar, at elevated T, the former are much stronger pinning sites leading to larger hysteresis and the presence of the peak. 相似文献
2.
A. P. Hope M. J. Naughton D. A. Gajewski M. B. Maple 《Physica C: Superconductivity and its Applications》1999,320(3-4):147-153
A series of avalanche-like jumps are observed in the mixed state of single crystal YBa2Cu3O7−δ (YBCO) superconductors. Emerging as a saw-tooth pattern in torque vs. sample orientation in magnetic field, these jumps are discontinuous on our most resolute angular scale. While reminiscent of the classical flux jump instability, the present jumps are instead proposed to be associated with the layered nature of the material and twin boundary (TB) pinning, the combination of which promotes a crossover from a tilted to a kinked vortex structure. 相似文献
3.
X.G. Zheng N. Mizuta H. Kuriyaki K. Hirakawa 《Physica C: Superconductivity and its Applications》1994,230(3-4):306-310
Tin and its oxides have been introduced into the intergrain areas of polycrystalline YBa2Cu3O7−δ by coating the crystalline grains with a thin layer of tin and sintering the ceramics in flowing oxygen and argon. The transport critical current density Jc at 77 K in a magnetic field of 0−1.5 T is enhanced as a result of the coating. A probable improvement of the intergrain weak links is suggested. 相似文献
4.
N. Watanabe K. Kuroda K. Abe N. Koshizuka M. Tagami Y. Shiohara 《Physica C: Superconductivity and its Applications》1998,300(3-4):301-308
The polarized Raman spectra of Nd1+xBa2−xCu3O7−δ (−0.023≤x≤0.107) and Pr1+xBa2−xCu3O7−δ (0.01≤x≤0.15) single crystals have been investigated. It was found that the Cu(2) Ag mode softens by 6 cm−1 in Nd 1:2:3 and 4 cm−1 in Pr 1:2:3 as x increases. These frequency shifts cannot be explained by the change in the relevant bond lengths due to Nd(Pr)-substitution for Ba. The variations with x of the two low frequency modes may be affected by change of their hybridization and/or change of their force constants. The linewidths of Ba mode in Pr 1:2:3 are broader than those in Y 1:2:3. This result suggests that the Pr substitution on Ba sites occurred even in a very small value of x. In x(yy)
geometry the relative intensity of the Ba and O(4) modes in Nd 1:2:3 is greater than those in Pr 1:2:3. The difference between Nd 1:2:3 and Pr 1:2:3 in the relative intensity of the Ba and O(4) modes may be produced by the chains. 相似文献
5.
YBa2Cu3O7−δ (YBCO) based SNS edge junctions with cobalt doped YBCO barriers were prepared and characterized. At 77 K, good junctions had RSJ-like I–V curves with excess current, magnetic suppression of Ic of about 50% or more, and clear microwave steps. The conductance values 1/RN at 77 K of junctions with different barrier thickness and composition, were proportional to the junction areas A, but show little correlation with the thickness of the barriers tB in the range of 15tB100nm. The corresponding IcRN products were observed to scale as J0.66±0.09c, similar to what was found by others. At the same time, the measured values of RN are much smaller than what is expected based on the dimensions of the junction and the resistivity of the barrier material. To explain all of this, we propose a model in which at high supercurrent densities, flux flow of Josephson vortices in the junction leads to RN values which are lower than expected. This model predicts
, which fits the observed results very well. 相似文献
Full-size image (1K)
6.
X. M. Xiong Z. Q. Peng Y. L. Zhou Z. H. Cheng H. B. Lu H. S. Wang D. F. Cui L. Li G. Z. Yang 《Physica C: Superconductivity and its Applications》1997,280(4):266-268
Our investigation on the relation between oxygen content and the laser-induced voltages of the YBa2Cu3O7−δ films in normal-state shows that deoxygenation of the superconducting films reduces the laser-induced voltages greatly, even reverses the sign of the signals at large oxygen deficiency. The absolute value of the negative signal at large oxygen deficiency can be greater than that of the positive signal. 相似文献
7.
M. W. Lee M. F. Tai H. J. Lee H. L. Hwang H. -C. I. Kao 《Physica C: Superconductivity and its Applications》1994,230(3-4):292-296
We report that the diamagnetism of as-grown YBa2Cu3O7−δ powders can be enhanced by treatment with RF-generated hydrogen plasma. The field-cooling susceptibility at 5 K is found to increase by up to 24%. The enhancement is reproducible for all five samples studied. The lattice parameter c decreases after hydrogenation. For a sample treated for the shortest period, its pinning potential,obtained from magnetic relaxation measurements, is reduced following H-treatment. 相似文献
8.
Influence of oxygen pressure on critical current density and magnetic flux pinning structures in YBa2Cu3O7-x fabricated by chemical solution deposition
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper studies the effect of oxygen partial pressure on the fabrication of YBa 2 Cu 3 O 7 x films on (00l) LaAlO 3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD).As the oxygen partial pressure increases to 1500 Pa,a great increase in the superconducting properties is observed at high magnetic fields parallel to the YBCO c axis.The cross-sectional transmission electron microscope images show that a high density of stacking faults in the size range of 10-15 nm may act as flux pinning centres to enhance the critical current density of the YBCO films 相似文献
9.
M. Jim nez-Melendo A. Domí nguez-Rodrí guez J. L. Routbort 《Physica C: Superconductivity and its Applications》1999,320(3-4):189-196
Rapid changes of oxygen partial pressure (PO2) between 103 and 2.1×104 Pa have been carried out during steady-state plastic deformation of polycrystalline YBa2Cu3O7−x (YBCO) at temperatures between 825 and 900°C. Transient creep was observed after such PO2 changes. The analysis of these creep transients allowed the determination of the chemical diffusion coefficient for reequilibration, which is identical to that found from thermogravimetry and electrical conductivity experiments for oxygen vacancies. 相似文献
10.
Hye-Soo Shin In-Sang Yang W. -C. Lee 《Physica C: Superconductivity and its Applications》1995,250(3-4):275-281
Single crystals with known Tc values of Y1−xPrxBa2Cu3O7−δ (Y---Pr1:2:3) and YBa2Cu3−xZn3−xZnxO7−δ (Y---Zn1:2:3) systems are studied by Raman measurements. The Raman spectra for (Y---Pr1:2:3) single crystals show that the frequencies of Ba and Oz modes increase as the Pr content increases. The results are consistent with the hole-localization scheme proposed for the suppression of superconductivity in the polycrystalline Y---Pr1:2:3 systems. On the other hand, in the Y---Zn1:2:3 system, all the Raman modes do not change in frequencies. However, the FWHM of the Cu(2) mode increases with the decrease of Tc, indicating strong scattering of charge carriers by the substituted Zn ions in the CuO2 planes. The induced disorder in the CuO2 planes may be related with suppression of Tc in the Y---Zn1:2:3 system. Thus, the suppression mechanism in the Y---Zn1:2:3 systems seems to be different from that in the Y---Pr1:2:3 systems. 相似文献
11.
Masahito Ban Katsumi Suzuki Youichi Enomoto 《Physica C: Superconductivity and its Applications》1997,290(3-4):345-353
SiO2 film coated as a passivation layer for YBa2Cu3O7−x (YBCO)-based microwave devices is investigated by measuring the microwave characteristics of microstrip line resonators. The SiO2 film is deposited with its 0.3 to 0.4 μm thickness by a sputtering method using Ar + 30%O2 plasma. These deposition conditions do not degrade the microwave characteristics and the critical temperature (Tc). Next, the SiO2 film coated resonators are compared with the uncoated ones for two kinds of degradation conditions: a 200°C annealing in air, and an exposure to air at 85°C and 85% RH (relative humidity). We find that the SiO2 passivation film prevents the YBCO thin film from the surface degradation and reacting with water. 相似文献
12.
We develop a theory of the critical current across grain boundaries in YBa2Cu3O7−δ bicrystals. Experiments have shown that there is hole depletion near a boundary and the concentration profiles have been determined for specific cases. These results mean that the critical temperature is a function of distance from the boundary. Taking this function from experiment as input into the theory, we study two specific boundaries: a boundary with a 7° misorientation angle about [100] which is known to be strongly coupled for the purposes of current flow, and a 31° boundary which is known to be weakly coupled. Using Ginzburg-Landau theory, we determine the dependence of the critical current density (jc) on temperature and the spatial dependence of the order parameter for these boundaries. The results show that the oxygen depletion can account for a major portion of the change from weak to strong coupling of boundaries as the misorientation angle is increased. 相似文献
13.
Dongliang Zhu Jie Huang Hui Li Mingrong Shen Xiaodong Su 《Physica C: Superconductivity and its Applications》2009,469(22):1977-1982
YBa2Cu3O7–δ (YBCO) films were prepared on (1 0 0) MgO substrates by pulsed laser deposition (PLD) method. In order to eliminate the a-axis growth, which is commonly observed in the YBCO film thicker than a critical value, we developed a new PLD target that was sintered at a temperature far below YBCO 123 phase formation. The surface analysis made by AFM technique confirmed that very fine particles of around 20 nm size could be ejected from the new target to the substrate. The fine oxide clusters could be easily moved and incorporated into the YBCO phase thus benefited the c-axis growth even in the thick films. For instance, only the c-axis growth in the new film with a thickness of about 650 nm was larger than a critical thickness of the a-axis growth. However, in the standard film of the same thickness, there is 24.5% of the a-axis growth accompanying the main c-axis growth. Therefore, the c-axis growth could be preserved in the very thick YBCO film by a non-superconducting target. 相似文献
14.
The behaviour of the hole number in YBCO systems as a function of the oxygen deficiency x is studied theoretically by calculating the density of electron states for several different superstructures formed by periodic arrangements of the oxygen vacancies. The characteristic features of the electronic properties for chain copper sites with different coordination are pointed out and their relevance in determining the number of carriers for oxygen planes is illustrated. It is shown that the curve of the hole number as a function of x shows plateaus and jumps similar to those found in the Tc versus x curves if the de-oxygenation process takes place by forming fragmented chains. Structures formed by filled and empty chains only give a smooth hole behaviour as a function of the composition. The results of the numerical calculations can be understood by a simple model giving the Fermi energy shift in terms of the concentrations of Cu(1) sites with different coordination. 相似文献
15.
R. Durny M. Puri L. Kevan
Y. J. Zhao
W. K. Chu 《Physica C: Superconductivity and its Applications》1992,190(4):460-464The modulated microwave absorption in YBa2Cu3O7−δ thin films was studied as a function of temperature, modulation amplitude, and microwave power. The comparative nature of weak links in YBaCuO thin films, ceramics, and powders is discussed. 相似文献
16.
H. Claus U. Gebhard G. Linker K. R hberg S. Riedling J. Franz T. Ishida A. Erb G. Mü ller-Vogt H. Wü hl 《Physica C: Superconductivity and its Applications》1992,200(3-4):271-276
X-ray diffraction, resistivity, AC and DC magnetization data on high-quality single crystals of YBa2Cu3O7−δ are presented. We demonstrate that for δ<0.08, the (0 0 l) diffraction lines are split into two, indicating that at these high oxygen concentrations the crystals are no longer single phase but actually consist of two (or more) different phases with slightly different c-axis parameters. In the two-phase region, the electrical resistivity and the AC and DC magnetic susceptibilities show a broadening of the superconducting transition. This broadening is thought to be due to the proximity effect or strains in two finely dispersed phases with slightly different transition temperatures. 相似文献
17.
Intercalation thermodynamics and chemical diffusion of oxygen in the solid solution YBa2Cu3−xCoxO6+δ
E. B. Mitberg M. V. Patrakeev A. A. Lakhtin I. A. Leonidov V. L. Kozhevnikov K. R. Poeppelmeier 《Solid State Ionics》1999,120(1-4):239-249
The equilibrium oxygen content as a function of the temperature and oxygen pressure was measured for the solid solution YBa2Cu3−xCoxO6+δ, where x=0, 0.2, 0.4, 0.6, 0.8, by using coulometric titration in the temperature range 600–850°C and oxygen pressures between 10−5 and 1.0 atm. The change in the partial molar enthalpy and entropy of the intercalated oxygen was determined at different oxygen and cobalt contents. The oxygen chemical diffusion was studied by thermogravimetric relaxation in the oxygen-controlled atmosphere. The thermodynamic data were employed to determine how the chemical diffusion coefficient, the thermodynamic factor and the random-diffusion coefficient depend on oxygen content in specimens with different cobalt concentration. The oxygen intercalation thermodynamics and diffusivity results provide evidence of ordering phenomena on a microscopic scale in the basal plane of the tetragonal solid solution YBa2Cu3−xCoxO6+δ. A model for the oxygen diffusion is suggested to explain the large difference between the random and tracer diffusion coefficients in YBa2Cu3O6+δ 相似文献
18.
D. Lpez E. A. Jagla E. F. Righi E. Osquiguil G. Nieva E. Morr F. de la Cruz C. A. Balseiro 《Physica C: Superconductivity and its Applications》1996,260(3-4):211-216
Transport measurements in the mixed state of oxygen-deficient YBa2Cu3O7−δ single crystals using the flux transformer configuration show that the flux liquid changes with increasing anisotropy from strongly correlated to uncorrelated in the field direction. For intermediate coupling, the current inducing loss of vortex correlation has a maximum near the irreversibility temperature. Thus, an effective softening of vortex lines with decreasing temperature is detected. We propose a simple model that accounts for this behavior by including the effects of the pinning potential on the dynamics of vortices. 相似文献
19.
C. C. Lam L. W. Shao X. Jin W. M. Chen H. Q. Xiong J. Feng S. R. Qi K. C. Hung 《Physica C: Superconductivity and its Applications》1996,270(3-4):333-342
In this paper, we have used the sputtering neutral-particles mass spectroscopy (SNMS) and positron-annihilation technique to investigate the effect of hydrogenation on the physical properties of different oxygenated YBa2Cu3O7−δ superconductors. Under the same of hydrogenation treatment, the hydrogenation effects on the superconductors are compared to the non-superconductors. It was shown that the hydrogen concentration in the superconductors is about eight times of the non-superconductor's. It was proven that the long lifetime of positrons in the annihilation process is determined by the variation of the concentrations of monovacancies and microvoids, which takes place in both of intragrain and intergrain samples. The hydrogenation effect can be classified into four stages. At the first stage, the hydrogen atoms fill both monovacancy and microvoid. At the end of the first stage, the long lifetime τ2 reaches the maximum value which is determined by the lifetime of the positron in the monovacancy-free and nearly microvoid-exhausted YBCO sample. In the second stage, the hydrogen charging will lead to creation of new monovacancies; this will make the long lifetime τ2 drop monotonically to its minimum value. In the third stage, further hydrogen charging promotes the formation of microvoids, and leads to an increasing τ2 up to a saturation value, which indicates the equilibrium concentrations of monovacancy and microvoid at that temperature. 相似文献
20.
V.S. Dang P. Mikheenko A. Sarkar M.M. Awang Kechik J.S. Abell A. Crisan 《Physica C: Superconductivity and its Applications》2010,470(20):1238-1241
We have investigated the superconducting properties of Ag/YBa2Cu3O7−x thick multilayers grown by Pulsed Laser Deposition, and found that the artificial pinning centres induced by Ag nanodots lead to a significant increase in critical current, especially in high applied magnetic fields. Transmission Electron Microscopy showed a columnar growth of YBa2Cu3O7−x induced by Ag nanodots, while angle-dependent transport measurements revealed the existence of strong, both isotropic and c-axis correlated, artificial pinning centres. 相似文献