共查询到20条相似文献,搜索用时 625 毫秒
1.
Soon-Gil Jung W.K. Seong N.H. Lee W.N. Kang 《Physica C: Superconductivity and its Applications》2011,471(21-22):798-800
We have investigated the flux pinning effect of columnar grain boundary in columnar-structured and single crystalline MgB2 films. The MgB2 films with columnar structure showed much higher Jc than that of single crystalline thin film, and sample having smaller grain size had a higher Jc in high magnetic fields. At 5 K, the MgB2 film with grain size of 460 nm showed an abnormal double-peak behavior in pining force density, Fp(B), caused by competition of different types of pinning sites, such as planar defects and point defects. Field dependences of Fp in columnar-structured films suggest that the columnar grain boundary is a strong pinning source in the MgB2 film and it plays a crucial role in enhancing Jc over a wide range of magnetic fields and temperatures. 相似文献
2.
T. Sueyoshi S. Yutani T. Sogo K. Yonekura A. Adachi T. Fujiyoshi F. Mitsugi T. Ikegami N. Ishikawa S. Awaji K. Watanabe 《Physica C: Superconductivity and its Applications》2010,470(20):1295-1299
We investigated the dependences of the critical current density Jc on the magnetic field angle θ in YBa2Cu3O7−δ thin films with the crossed configurations of the columnar defects (CDs). To install the crossed CDs, the films were irradiated using the high energetic Xe ions at two angles relative to the c-axis. The additional peak around the c-axis appears in the Jc(θ) for all irradiated films. In lower magnetic fields, the height of the Jc(θ) peak caused by the crossed CDs with the crossing angles θi = ±10° was higher than that for the parallel CDs. It is considered that the correlation of the flux pinning by the crossed CDs along the c-axis occurs even in the case of θi = ±25°, which was also suggested by the kink behaviors of the scaling parameters of the current–voltage characteristics near 1/3 of the matching field. In higher magnetic fields, on the other hand, the height and width of the Jc(θ) peak for the crossed CD configurations rapidly reduce with increasing the magnetic field compared to the parallel ones. In the crossed CD configurations, the dispersion in the direction of CDs would prevent the correlation of flux pinning along the c-axis in high magnetic fields, which occurs in the parallel CD configurations due to the collective pinning of flux lines including the interstitial flux lines between the directly pinned flux lines by CDs. 相似文献
3.
D.H. Kim Jun-Ki Chung T.J. Hwang W.N. Kang Kook Chae Chung 《Physica C: Superconductivity and its Applications》2009,469(21):1950-1953
We measured the transport properties of MgB2 films having columnar grain structure with their axis normal to the substrate. When an external magnetic field was applied parallel to the grain axis, an enhanced critical current density has been observed, and this result has been ascribed to flux pinning induced by grain boundaries. The shape of the angular dependence of critical current density and its magnetic field dependence showed a quite similar resemblance to those of YBa2Cu3Ox films containing columnar defects, implying a possible existence of linear defects in MgB2 films of columnar structure. We propose that the amorphous regions at the vertex points of three or more grain boundaries observed in microstructural studies correspond to the linear defects and these linear defects anchor the end points of the flux line dislocations of Frank-Read sources, by which the shear in the flux line lattice is actuated. This assumed mechanism is found to reasonably explain the magnetic field dependence of the flux pinning force density of MgB2 films with columnar grain structure. 相似文献
4.
M. Inoue R. Fuger K. Higashikawa T. Kiss M. Namba S. Awaji K. Watanabe A. Ibi S. Miyata Y. Yamada T. Izumi 《Physica C: Superconductivity and its Applications》2010,470(20):1292-1294
We have investigated current transport property in Gd1Ba2Cu3O7−δ coated conductor with artificial pinning centers in a wide range of temperature, magnetic field, B up to 27 T, and field angle. Due to the additional c-axis correlated pins, critical current density, Jc in B//c was enhanced and the improvement was observed in wide range of B. On the other hand, around B⊥c below 65 K, the angular dependence of n-value showed a valley-like behavior, although the Jc was increasing. In addition, the temperature dependence of the pinning force density defined as Jc × B was not scaled on an expected master curve. These results indicate the pinning in B⊥c is governed by different mechanism below 65 K and high magnetic field. 相似文献
5.
《Current Applied Physics》2018,18(6):762-766
We report a facile method to enhance the critical current density (Jc) of superconducting MgB2 thin films. MgB2 thin films were deposited on zinc acetate dehydrate (Zn(CH3COO)22H2O) spin-coated Al2O3 (000l) substrates by using a hybrid physical-chemical vapor deposition system at low temperatures. Synthesis of MgB2 at low temperatures can reduce the substitution of Zn into the Mg site, hence avoiding the reduction of superconducting critical temperature. MgB2 thin films grown on ZnO-buffered layers showed a significant enhancement of Jc in the magnetic field due to the creation of additional pinning sources, namely point defects and grain boundaries. Broad peaks were observed in the magnetic field dependence of the flux pinning force density, indicating competition of different pinning sources. 相似文献
6.
D. Ahmad I. Park G.C. Kim J.H. Lee Z.-A. Ren Y.C. Kim 《Physica C: Superconductivity and its Applications》2009,469(15-20):1052-1054
The irreversibility line and flux pinning properties of high-Tc superconductor SmFeAsO0.85 were studied using DC magnetization data. Polycrystalline SmFeAsO0.85 was prepared in a high pressure synthesis apparatus under the pressure of 6 GPa. The results of DC susceptibility showed the superconducting transition at about 55 K. A critical current density Jc(B) was calculated using Bean’s critical state model. At low temperatures (20 K), Jc(B) showed a relatively high value with weak dependence on an applied magnetic field. At higher temperatures, a stronger dependence of the magnetic field was observed, which resulted from decrease in a critical current density probably due to the flux creep effect. The irreversibility line (IL) agreed well with the flux creep theory of Matsushita et al. A comparison of normalized pinning force density with the theoretical models showed that the irreversible behavior in SmFeAsO0.85 is dominated mainly by normal point pinning (δTc) and surface pinning mechanisms. 相似文献
7.
R. Goswami T.J. Haugan P.N. Barnes G. Spanos R.L. Holtz 《Physica C: Superconductivity and its Applications》2010,470(5-6):318-322
In pulsed laser deposition of YBa2Cu3O7?δ films, defect introduction into the films tends to anisotropically improve the pinning along the H||c direction due to the columnar growth mode of the process. In Eu-substituted samples, however, even though an increase in critical current density (Jc) in the H||c direction was observed for low fields (H = 0.2 T), the improvement was more notable for the H||ab-plane at both low and higher fields. Herein we present detailed TEM microstructural studies to understand these new trends in Jc(H), which are markedly different than flux pinning increases achieved with other methods, for example, with nanoparticle additions. Threading dislocations, observed in the Eu-substituted samples along the c-axis, account for Jc enhancement with H||c at low field. The enhanced ab-planar pinning in the Eu-substituted samples is attributed to the extensive bending of the {0 0 1} lattice planes throughout the film, and the crystal lattice defects with excess Cu–O planes, that were effective in increasing the Jc for H||ab at both low and high fields. 相似文献
8.
R. Teranishi Y. Miyanaga K. Yamada N. Mori M. Mukaida M. Miura M. Yoshizumi T. Izumi M. Namba S. Awaji K. Watanabe 《Physica C: Superconductivity and its Applications》2010,470(20):1246-1248
Tin-compounds were doped into YBa2Cu3O7−δ (YBCO) films as pinning centers to enhance Jc in magnetic fields. YBCO films were grown by a metal organic deposition process using tri-fluoroacetates starting solutions. Tin-acetylacetonate salts were then dissolved into the starting solution as pinning centers. Jc of the YBCO films with tin-acetylacetonates were enhanced in all magnetic field angles. Transmission electron microscopy (TEM) and TEM-EDS (Energy Dispersive X-ray Spectroscopy) observations revealed the existence of tin-compound particles with the size of about 30 nm in the YBCO film. These nano particles were distributed randomly in the film and were considered to act as 3-dimentional pinning centers. 相似文献
9.
On the research and development of coated conductors in Japan, the Ic characteristics and the length have been remarkably improved in the national project. Five hundred meter-long tapes with higher Ic values than 300 A/cm-width were realized by the pulsed laser deposition (PLD) and the metal organic deposition using trifluoroacetates (TFA-MOD) processings for the superconducting layer on the IBAD-GZO buffered substrates. In order to realize the low cost by the increasing the production rate of the ion beam assisted deposition (IBAD) layer, the process of IBAD-MgO was developed and a 1000 m-long IBAD buffer tape was fabricated at an extremely high production rate of 1 km/h. On the other hand, the artificial pinning center has been introduced in both PLD and MOD processing. The BaZrO3 nano-rods were aligned along the c-axis of GdBCO superconducting films by the PLD process. The Jc value in the magnetic field parallel to the c-axis was remarkably improved. Additionally, the BaZrO3 nano-particles were uniformly dispersed in YGdBCO films by the TFA-MOD process and the Jc–B–θ property was confirmed to be isotropic. 相似文献
10.
K.R. Mavani D.S. Rana S. Rayaprol R.N. Parmar Ravi Kumar J. John 《Solid State Communications》2007,142(8):462-465
We have deposited c-axis oriented thin films of La1.5Dy0.5CaBa2Cu5Oz (La-2125) tetragonal superconductor on LaAlO3(001) substrates by pulsed laser deposition. These films were irradiated with 200 MeV Ag+15 ions. Atomic force microscopy and elastic recoil detection analysis indicate that the irradiation has created columnar defects through the entire thickness (2000 Å) of these films. With ion irradiation up to 1×1011 ions/cm2, the critical current density (Jc(H)) enhances by fivefold, which is attributed to the augmented flux pinning by the columnar defects. A further increase in irradiation to 1×1012 ions/cm2 causes reduction in Jc(H) due to distorted morphology of the film. Our work shows that the enhancement in Jc(H) of the irradiated La-2125 film is comparable to that in irradiated RE-123 (RE = rare earth ion). Also, as the La-2125 type films have greater chemical stability than RE-123, La-2125 type superconductors are potential candidates for applications. It is interesting to note that there are partial flux jumps observed to occur symmetrically in the magnetic hysteresis of irradiated La-2125 thin films with enhanced Jc(H). 相似文献
11.
12.
Ch. Neumann Ch. Heinzel P. Ziemann K. Fischer W. Gawalek 《Zeitschrift für Physik B Condensed Matter》1991,84(1):37-42
High quality flux grown and defect enriched peritectically grown YBa2Cu3O7–x single crystals have been investigated by an ac-susceptibility technique. This method allows to determine an irreversibility line from the temperature and field dependence of the peaked imaginary part of the susceptibility, which is due to magnetic losses. For magnetic fieldsH
ac perpendicular to thec-axis of the crystal, the irreversibility line of the defect enriched crystal shows a shift to higher field values as compared to the perfect crystal, a sign that crystal defects like Y2BaCuO5(211)-precipitates and microcracks act as strong pinning centers. ForH
ac parallel to thec-axis no clear evidence for a stronger pinning is found. From these results we conclude that different pinning mechanisms are dominating at different field orientations. 相似文献
13.
《Physica C: Superconductivity and its Applications》2007,451(1):71-76
The stoichiometry dependence of the microstructure and superconducting properties of pure and nano-SiC doped MgB2/Fe tapes was systematically investigated. The tapes prepared with the composition of a slight deficiency of Mg (Mg0.9B2 and MgxB2(SiC)0.1 (x = 0.9 and 1.0)) showed the best transport Jc. Adding a slight excess of Mg like 5%, as being done by many researchers, was not beneficial for the Jc improvement as expected. The onset Tc was not significantly changed in both doped and undoped tapes by adding excess of boron or magnesium, but the transition widths were broadened due to the induced impurities. The slightly-Mg-deficient pure samples show smaller grain sizes, which corresponds to a better Jc–B performance at high magnetic field due to the enhanced grain boundary pinning. The field dependence of Jc in nano-SiC doped tapes was almost not influenced by varying the starting Mg content although microstructural difference can still be seen, suggesting that the flux pinning ability was mainly controlled by the carbon substitution effect for boron. 相似文献
14.
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
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
15.
Y.-F. Zhao Y.-H. Zhou 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):391-396
The influence of non-uniform Jc distributions on flux
jumps in high-temperature superconductors is investigated with the
simplified models in the form of a composite superconducting slab consisting
of different pinning regions. The magnetization loops and flux jumps for the
simplified models are calculated with the modified recursion formulas which
could predict the flux-jump fields. The valid ranges of the temperature and
sweep rate for Bfj1 are specified and the fields of the subsequent
jumps after the first flux jump of the inhomogeneous models are obviously
lower than that of the homogeneous models. The results indicate that flux
jump instability could be stimulated by non-uniform Jc distributions and
with the increase of the discrepancy of Jc between different pinning
regions the instability also increase. 相似文献
16.
In this paper we aimed at investigating the flux pinning property of MgB2 films on hastelloy tapes which are buffered on various thicknesses of SiC layers. We have observed that the increase in thickness of the SiC buffer layer is very closely related with the systematic improvement of the field dependence of the critical current densities (Jc) of MgB2 tapes while the values of Jc decreased. According to the analysis of the pinning force density (Fp), there exist two pinning sources both in the pure MgB2 and in the MgB2 film with the thinnest SiC buffer layer. On the while, the pinning source observed in the MgB2 films with thicker SiC buffer layers appears to be different from those previously mentioned. The different pinning behaviors of MgB2 films may suggest that there be an additional pinning center working on the MgB2 films with thick SiC buffer layers. The microstructural analyses of MgB2 films confirmed that intra-granular defects and columnar grain boundaries may be a dominant pinning mechanism in the pure MgB2 and the MgB2 film with 170 nm-thick SiC buffer layer. For the MgB2 films with thicker SiC buffer layers, carbon diffusion into the MgB2 film, which is defined by the Auger electron spectroscopy, may be the origin of the additional pinning mechanism. 相似文献
17.
Ying Tang Xiangjie Kong Jianlian Zang 《Physica C: Superconductivity and its Applications》2009,469(21):1902-1905
The Cu-doped MgB2 bulks were prepared by a high-energy milling and subsequent sintering method. Compared to the pure and Cu-doped bulks prepared only by sintering, the critical current density (Jc) of the milled Cu-doped samples was improved with a slight decrease in critical transition temperature (Tc). Using the phase analysis and microstructure observation, it has been found that the MgB2 grains in the milled Cu-doped sample was refined with the high-energy milling and thus provided more grain boundary pinning, which was contributed to the improvement of Jc at high field. 相似文献
18.
M. Ciszek K. Rogacki K. Oganisian N. D. Zhigadlo J. Karpinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(3):359-365
The DC magnetization and AC complex magnetic
susceptibilities were measured for MgB2 single crystals, unsubstituted
and carbon substituted with the composition of
Mg(B0.94C0.05)2. The measurements were performed in AC and DC
magnetic fields oriented parallel to the c-axis of the crystals. From the DC
magnetization loops and the AC susceptibility measurements, critical current
densities (J
c were derived as a function of temperature and the DC and
AC magnetic fields. Results show that the substitution with carbon decreases
J
c
) at low magnetic fields, opposite to the well known effect of an
increase of J
c
at higher fields. AC magnetic losses were derived from
the AC susceptibility data as a function of amplitude and the DC bias
magnetic field. The AC losses were determined for temperatures of 0.6 and
0.7 of the transition temperature T
c
, so close to the boiling points of
LH2 and LNe, potential cooling media for magnesium diboride based
composites. The results are analyzed and discussed in the context of the
critical state model. 相似文献
19.
T. Naito K. Sato D. Yamaguchi H. Fujishiro 《Physica C: Superconductivity and its Applications》2009,469(15-20):1218-1220
We have studied the effect of a small amount of Y-site substitution by La or Pr ions on the vortex pinning in the Y–Ba–Cu–O system. (Y1-xLax)–Ba–Cu–O and (Y1-xPrx)–Ba–Cu–O bulks were fabricated by the melt-textured growth, in which x was varied from 0 to 0.01. The critical current density Jc at 77 K is improved in magnetic fields parallel to the c-axis above 2–4.5 T and the corresponding irreversibility field, Hirr, shifts to the higher value in both bulks. 相似文献
20.
Y. Yang C.H. Cheng L. Wang H.H. Sun Y. Zhao 《Physica C: Superconductivity and its Applications》2010,470(20):1100-1102
In this paper, we study the doping effect of sorbic acid (C6H8O2), from 0 to 20 wt.% of the total MgB2, on critical temperature (Tc), critical current density (Jc), irreversibility field (Hirr) and crystalline structure. The XRD patterns of samples show a slightly decrease in a-axis lattice parameter for doped samples, due to the partial substitution of carbon at boron site. On the other hand, we investigate the influence of doping on the behavior of flux pinning and Jc(B) in the framework of percolation theory and it is found that the Jc(B) behavior could be well fitted in high field region. The two key parameters, anisotropy and percolation threshold, play very important roles. It is believed that the enhancement of Jc is due to the reduction of anisotropy in high field region. 相似文献