共查询到20条相似文献,搜索用时 15 毫秒
1.
Zhengping Qin Gang Jin Chuanbing Cai Shixun Cao Xin Yao Jincang Zhang 《Journal of Superconductivity and Novel Magnetism》2009,22(4):373-379
Pr-doping Y0.928Pr0.072Ba2Cu3O7−δ
superconducting single crystal was studied systemically by the magnetic response measurement below T
c
. DC magnetization shows a possible existence of micro-phase separation caused by the non-uniform distribution of Pr ions
in microstructure during the growth procedure. The magnetic field dependence of critical current density J
c
and pinning force density F
p
had been obtained from the magnetization hysteresis loop. Flux pinning mechanisms in different magnetic fields had been discussed
using the scaling function as well as the ratio of the pinning force field at H
on and H
peak. We find that the peak effect is influenced by the micro-phase separation which is caused by the non-uniform distribution
of Pr ions in microstructure during the growth procedure. The interface between the different T
c
superconductivity areas can be the effective pinning center which is useful to the appearance of peak effect. The value of
the ratio of the maximum pinning force field to the irreversibility field is discussed. The conclusion is consistent with
the model constructed by Wen et al.; we finally draw out the thermomagnetic phase diagram for our samples.
相似文献
2.
N. Ishikawa A. Iwase T. Iwata H. Maeta K. Tsuru O. Michikami 《Journal of Superconductivity》1994,7(1):241-242
The effect of He ion irradiation on the pinning potential in EuBa2Cu3O
y
, thin film was investigated by measuring the temperature dependence of resistivity in magnetic fields. The pinning potential decreased as the ion fluence increased. A slower decrease of pinning potential was observed in higher magnetic field in the fluence region <3.5×1015 cm–2. 相似文献
3.
We have studied the role of short relaxation time on magnetic hysteresis in a Bi2Sr2CaCu2O
x
single crystal. Effects were examined by comparing isothermal magnetization curves obtained over a range of temperatures as a function of the applied magnetic field, H, for magnetic field ramp rates of 3 and 30 Oe/s. At low temperature, a second magnetization peak, H
p, was produced by differences in magnetic relaxation occurring over a short period during the initial stage of relaxation. The data suggested an absence of pinning crossover for H H
p. 相似文献
4.
Magnetic relaxation, with magnetic fields applied parallel to the c axis, was measured in a high-quality melt-textured YBa2Cu3Ox bar. Zero-field-cooled magnetization-versus-time data were obtained within a regime of field and temperatures dominated by single vortex pinning. The activation pinning energy U = U
M
was calculated from experimental data and compared to U = U
0
ln(J
c
/J), where U, is a constant, J
c
is the critical current density, and J the current density. This expression for U obtains within the individual pinning regime. A logarithmic dependence of U
M
on J was found, and the data indicated that a scaling function of U
M
, g(T/T
c
) = (1–T/T
c
)1/2, was appropriate for describing the single-vortex pinning regime. 相似文献
5.
We present DC magnetization data indicating a first-order phase transition in the vortex state of CeRu2, with the higher entropy phase exhibiting enhanced pinning. Minor hysteresis loops show evidence of supercooling of the higher
entropy phase as the phase boundary is crossed both isothermally as well as at constant field. These features are shown to
be absent across the Bragg-glass to vortex-glass transition in Bi2Sr2CaCu2O8. The supercooling is more persistent in the constant field case. 相似文献
6.
The superconducting properties of iodine-intercalated high-temperature superconducting Bi2Sr2Ca2Cu3O10+x
phase (Bi-2223) were systematically studied. It was found that for samples containing a significant amount of Bi2Sr2CaCu2O8+x
, iodine intercalation results in the dramatic decrease of the inter-granular critical current density, as well as a significant
decrease of the critical temperature (T
c), the critical current density in the grains (J
cg), and of the amount of Bi-2223. For samples with a large amount of Bi-2223, T
c changes insignificantly, whereas J
cg can even increase. We argue that the different behavior of the superconducting parameters is the result of various oxygen
concentrations, and we explain the effect of iodine intercalation based on the parabolic dependence between T
c and the number of holes per CuO2 layer. The H(T) curves (determined from the peak position in the loss signal of ac susceptibility) for intercalated samples deviate significantly
from the quasi 2D-like behavior, pointing toward an enhancement of the 3D fluctuations of vortices. For the change in the
values and dimensionality of the flux pinning in the process of the intercalation, we attempted a qualitative explanation
based on the models proposed in literature. 相似文献
7.
通过溶胶-凝胶法制备单相Bi2Sr2Co2Oy化合物,通过添加PEG20000和超声分散对化合物粉体微结构进行调控,采用SPS烧结得到了致密的块体.探索了微结构对Bi2Sr2Co2Oy化合物电性能的影响规律.结果表明,添加PEG20000和超声分散可以明显降低Bi2Sr2Co2Oy化合物粉体的晶粒尺寸,使烧结块体的晶粒尺寸大幅度减小,从而显著提高材料的电性能.温度为873K时,添加PEG20000并超声处理所制备样品烧结块体获得了最高ZT值0.041. 相似文献
8.
Q. Liu S. L. Wen D. S. Yan M. H. Fang Z. K. Jiao Q. R. Zhang 《Journal of Superconductivity》2000,13(1):73-76
Considerably improved flux pinning and critical current density J
c values have been achieved in Y-deficient Y-123 superconductors by directional solidification in air. In comparison with the regular Y-123 composition, Y-deficient one also has an orthorhombic structure and Y-123 main crystal phase remains in it. Whereas with the shortage of Y, Y1–x
Ba2Cu3O7–y can be regarded as (YBa2Cu3)1–x
O7–t(Ba2Cu3)
x
O
t–y
or (YBa2Cu3O7–z
)(
x
YO
z–y
), so there may develop several kinds of microstructure defects as pinning sites in the system, such as highly dense, fine-scale, and faultlike defects, as well as localized superstructure, which are able to induce the increasing in flux pinning and J
c values in higher external magnetic fields. This kind of simple nonstoichiometric route could lead to a commercial technique for flux-pinning enhancement in Y-123 bulk materials. 相似文献
9.
S K Arora Ravi Kumar D Kanjilal G K Mehta S Khatua R Pinto Vijay Kumar A K Gupta 《Bulletin of Materials Science》1999,22(3):251-255
Effect of 250 MeV107Ag ion irradiation induced columnar defects on the noise properties of the YBCO superconductor in the normal and superconducting
state have been investigated. Magnitude of the spectral density of the noise is found to scale inversely with the frequency
and exhibit a quadratic dependence on the bias current confirming that the noise arises due to the resistance fluctuations.
The magnitude ofS
v has been found to decrease with decrease in temperature and shows a noise peak in the transition region. The noise performance
of these materials in the vicinity of the superconducting transition as well as in the normal state is found to improve by
an order of magnitude after irradiation with 250 MeV107Ag ions. The decrease in the magnitude of 1/f noise peak is due the irradiation induced enhanced flux pinning of the material which suppresses the flux motion induced
noise in the vicinity ofT
c. 相似文献
10.
G. Balestrino D. Fiorani P. Paroli J. Tejada A. M. Testa 《Journal of Superconductivity》1990,3(2):211-214
The anisotropy of critical current densityJ
c
in Bi2Ba2CaCu2O8+x
single crystals has been investigated as a function both of the temperature and of the applied magnetic field. An anisotropic behavior ofJ
c
has been found. The decay of the remanent magnetization has been studied for fields applied both parallel and perpendicular to thec axis. A logarithmic behavior was found. A pinning energyU
0 of about 0.01 eV, independent of the direction of the applied field, was obtained. 相似文献
11.
Bo Cheng Tony Ragsdale W. J. Yeh 《Journal of Superconductivity and Novel Magnetism》2008,21(5):289-296
Enhancing the pinning force in high-T
c superconductors can be achieved by externally introduced periodic magnetic dots. We numerically calculate the interaction
between ferromagnetic dots and vortices in high-T
c superconductors. The London equation is used to generate two-dimensional vortex lattice. In the matching condition, we calculate
the attraction force between magnetic dots and vortices. It is found that in an ideal condition, the pinning force of the
magnetic dot reaches 2.5×10−11 N that is more than one order magnitude stronger than the intrinsic pinning force in YBa2Cu3O7 thin films. In the experimental side, we use a novel nano-technique to deposit periodic submicron Ni dots on YBa2Cu3O7 thin films. The current versus voltage characteristics of an YBa2Cu3O7 thin film strip with uniform Ni dots are measured at various temperatures and magnetic fields. They are compared with the
current versus voltage characteristics of a bare YBa2Cu3O7 thin film strip without magnetic dots. It is found the critical current value of the strip with Ni dots reduces with a much
slower pace as the magnetic field strength increases in comparison with the value of the bare sample. 相似文献
12.
M. Muralidhar M. Jirsa N. Sakai M. Murakami I. Hirabayashi 《Materials Science and Engineering: B》2008,151(1):90
The Jc and Hirr values at 77 K of ternary light-rare-earth compounds, LREBa2Cu3Oy “LRE-123”, are usually high enough to serve in various applications. Several sources of vortex pinning can be in these composites tailored to fit the needs of the particular application. The list comprises LRE/Ba solid solution, oxygen vacancies, large particles of secondary phases, twin planes, nanoscale lamellas, etc. By means of the latter defects one can achieve a very high irreversibility field. Refinement of secondary phase particles and the optimal choice of their amount enhance the electromagnetic performance in a broad temperature range, up vicinity of Tc, allowing levitation at liquid oxygen, 90.2 K. An optimum content of MoO3 doubles the self-field super-current at 77 K, H||c-axis. Altogether, the pinning tailoring in ternary LRE-123 materials provides a flexible and reliable way to fit the electromagnetic performance with the needs of sophisticated high-temperature and high-magnetic-field applications. 相似文献
13.
A. Ya. Basovich R. K. Belov V. A. Markelov V. V. Talanov 《Journal of Superconductivity》1995,8(1):121-123
The magnetic field dependence of the surface impedance (resistance and reactance) of high-T
c
thin films is found employing measurements of the quality factor and the frequency of the parallel plate resonator in a dc magnetic field up to 500 Oe at 10 GHz.c-Oriented YBa2Cu3O7 thin films are examined. Enhancement of surface resistance and inductance with increase of magnetic field is observed. The effect of irreversible increase of surface impedance as compared to its initial values after a cycle of magnetic field commutation is found. A qualitative explanation of the observed effects based on the picture of magnetic vortex penetration and accumulation in the film due to strong pinning is presented. 相似文献
14.
Valery A. Cherenkov 《Journal of Superconductivity》1991,4(6):429-430
A phase diagram of new high-T
c
superconductors as highly pinning superconductors of the second type is presented. The diagram includes both vortex glass and vortex liquid phases. 相似文献
15.
J. H. Park S. W. Kim S. H. Lee H. S. Kim S. S. Park H. C. Park 《Journal of Materials Synthesis and Processing》2002,10(5):289-293
Alumina (Al2O3) powders were synthesized by extracting Al2O3 from kaolin via kaolin-H2SO4 reactions with and without ultrasounds. The amount of Al2O3 extracted from kaolin via the ultrasonic extraction process was investigated by comparing reaction time and reaction temperature with the same factors under the conventional extraction process. The time to obtaining a given amount of Al2O3 by the ultrasonic process was shorter than that by the conventional process, indicating that the application of ultrasound in the synthesis of Al2O3 powders is an efficient way to reduce synthesizing time. 相似文献
16.
K. P. Singh V. P. S. Awana S. Balamurugan M. Shahabuddin H. K. Singh M. Husain H. Kishan E. R. Bauminger I. Felner 《Journal of Superconductivity and Novel Magnetism》2008,21(1):39-44
Nano particle of Fe3O4 (nFe3O4) up to 6 at% were doped in the superconducting MgB2 samples. Despite the strong ferromagnetic nature of Fe3O4, both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe3O4, T
c
=38 K is not changed, whereas for 6% T
c
decreases by 6 K. This indicates that a low concentration of Fe does not substitute either the Mg or B sites and probably
occupies the intergrain spaces. For 0.5% doped Fe3O4, an increase in J
c
with respect to the pure MgB2 samples is observed in the lower field and temperature regions (H<2 T and 20 K) indicating an enhanced flux pinning and the magnetic activation, i.e., the interaction between the magnetic
dipole of Fe ion and the vortices is weak in comparison to the effective pinning potential. Whereas, at H>2 T, J
c
of the doped samples is always less than that of MgB2, and the activation is dominant in comparison with the effective pinning potential provided by the doping. Flux jumps are
observed in lower T and H regions for the samples doped up to 1% nFe3O4 only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for
the higher (4, 6 at%) nFe3O4 doped MgB2 samples show that at RT, the hyperfine field for both samples is ∼100 kOe and ∼120 kOe at 90 K. This means that the nFe3O4 particles decompose and form possibly an intermetallic Fe-B phase in the matrix. 相似文献
17.
The CaTiO3 and La-doped CaTiO3 [Ca1–x
(La)
x
TiO3, x = 0.05–0.3] powders were prepared from aqueous solutions by the ultrasonic mist pyrolysis and ultrasonic mist combustion processes. Glycine provides carboxylic acid and amine groups as a fuel in the ultrasonic mist combustion process. In ultrasonic mist pyrolysis, the particles with hollow sphere morphology were obtained; whereas, particles prepared by the ultrasonic mist combustion process had a dense solid morphology with low porosity. The ultrasonic mist combustion process using metal nitrates and glycine as the fuel for a starting material has proved to be a simple and unique approach to preparing dense CaTiO3 powder and a solid solution of CaTiO3 with lanthanum. 相似文献
18.
M. Pissas E. Moraitakis D. Stamopoulos G. Papavassiliou V. Psycharis S. Koutandos 《Journal of Superconductivity》2001,14(5):615-621
We present a modified method of preparation of the new superconductor MgB2. The polycrystalline samples were characterized using X-ray and magnetic measurements. The surface barriers control the isothermal magnetization loops in powder samples. In bulk as prepared samples we always observed symmetric magnetization loops indicative of the presence of a bulk pinning mechanism. Magnetic relaxation measurements in the bulk sample reveal a crossover of surface barrier to bulk pinning. 相似文献
19.
Elif Emil 《Materials Science & Technology》2018,34(13):1549-1557
ABSTRACTYttrium oxide (Y2O3) particles were synthesised from a yttrium nitrate solution via ultrasonic spray pyrolysis (USP) method. The effects of temperature and precursor concentration on morphology and microstructural parameters were investigated. Y2O3 particles were characterised by scanning-electron-microscope energy-dispersive spectroscopy, Raman spectroscopy and X-ray diffraction analysis. Based on X-ray peak broadening, the crystallite size was calculated using the modified Debye–Scherrer (MDS) method. Furthermore, the crystallite size, crystal strain and the energy density of the crystal were evaluated using the Williamson–Hall (W–H) analysis integrated with the uniform deformation model, the uniform stress deformation model and the uniform deformation energy density model. A comparative evaluation of Y2O3 crystallite size using the MDS and W–H methods was carried out.This is part of a thematic issue on Nanoscale Materials Characterisation and Modeling by Advances Microscopy Methods - EUROMAT. 相似文献
20.
The temperature dependence of the critical current density at high temperatures and in weak applied magnetic field for YBa2Cu3O7–y
ceramic samples with a pronounced granular character is analyzed. The experimental results can be explained in terms of thermally activated motion of the intergrain Josephson vortices at grain boundaries, which may be an indication that the actual limiting factor for the critical current density in ceramic samples results from a weak pinning force density for the intergrain vortices rather than from the weak-link quenching. 相似文献