共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
A. Talapatra S. K. Bandyopadhyay Pintu Sen A. Sarkar P. Barat 《Bulletin of Materials Science》2004,27(5):429-432
MgB2 superconductor has been synthesized using a simple technique at ambient pressure. The synthesis was carried out in helium
atmosphere over a wide range of temperatures. Magnesium was employed in excess to the stoichiometry to prevent the decomposition
of MgB2. Samples of MgB2 thus prepared have been almost free from MgO as compared to other methods. Resistivities of the samples are quite low with
residual resistivity ratio (RRR) of around 3.T
c
(R = 0) is 38.2-38.5 K with ΔT
C of 0.6–1.0 K. Comparative studies of various methods of low pressure synthesis have been presented. 相似文献
3.
Superconducting bulks of MgB2 with addition of Sb2O3 and Sb with different stoichiometric compositions ((MgB2) + (Sb2O3)
x
, x = 0.0025, 0.005, 0.015, and (MgB2) + (Sb)y, y = 0.01) were obtained by the Spark Plasma Sintering (SPS) technique. All added samples have high density, above 95% and critical
temperature, T
c, of 38.1–38.6 K. This result and XRD data suggest that Sb does not enter the lattice of MgB2. Impurity phases are Mg3Sb2, MgO, and MgB4. The optimum addition is Sb2O3 for x = 0.005. This sample shows the critical current density, J
c(5 K, 0 T) = 4 × 105 A/cm2 and J
c(5 K, 7 T) = 6 × 102 A/cm2, while the irreversibility field, H
irr (5 K, 100 A/cm2) = 8.23 T. Indicated values of J
c and H
irr are higher than for the pristine sample. The mechanism of J
c and H
irr increase in the Sb2O3 added samples is complex and composed of opposite effects most probably involving morphology elements, the presence of nano
metric MgB4 and the indirect influence of oxygen or oxygen and Sb. Crystallite size of MgB2 is decreasing when Sb-based additions are introduced and the effect is stronger for the Sb-metal addition. The sample with
Sb-metal addition does not improve J
c and H
irr when compared with pristine sample. 相似文献
4.
K. Q. Ruan Z. M. Lv H. Y. Wu S. L. Huang M. Li Z. Q. Pang Q. Y. Wang Y. Feng G. Yan 《Journal of Superconductivity and Novel Magnetism》2008,21(4):237-242
The doping effect of amorphous carbon (C) containing magnetic impurity in MgB2 bulk has been studied. Structural characterization by means of X-ray diffraction and the superconducting transition temperature,
T
c
, measurement indicate that little C effectively enters the MgB2 structure. This should be due to the lower sintering temperature. The upper critical field, H
c2, and irreversibility field, H
irr, of samples show no systematic evolution with C doping. However, critical current density J
c
(H) performance is greatly improved with C doping at 4, 15, and 28 K, respectively. Corresponding to this case, scanning electron
microscope (SEM) image indicates that the grain size in samples becomes very small and grain boundary is developing roundness
with the increasing of C content. This should be intimately related with the increase of magnetic impurity along with C doping.
The result is discussed.
相似文献
5.
X. F. Pan C. H. Cheng Y. Zhao 《Journal of Superconductivity and Novel Magnetism》2011,24(5):1611-1616
A series of rare-earth-oxide-doped MgB2 bulks are prepared by in situ solid-state reaction with Pr6O11, CeO2, Lu2O3, and Ho2O3 as the dopants. The superconducting properties are investigated and compared with the nano-Fe3O4 doped MgB2. It is found that different from doping ferromagnetic nano-Fe3O4 which drastically suppresses superconductivity of MgB2, doping the rare-earth-oxides has little effect on superconductivity of MgB2 although most rare-earth elements have strong magnetic moment. In addition, some boride impurities formed during the reaction
between rare-earth oxides and boron can work as effective pinning centers and significantly improve J
c and H
irr of MgB2 when these fine nanoboride precipitates (<20 nm) are embedded into the MgB2 intragrains. 相似文献
6.
Jinyuan Ma Aimin Sun Guidan Wei Long Zheng Guofeng Yang Xiu’e Zhang 《Journal of Superconductivity and Novel Magnetism》2010,23(2):187-191
A series of polycrystalline Al doped Mg1−x
Al
x
B2 (x=0.00, 0.01, 0.03, 0.06, 0.10, 0.15) samples were prepared using the solid-state reaction route. Phase analysis showed that
Al is alloyed into the MgB2 lattice and there were some Al2O3, MgAlB4 particles present in bulk samples of MgB2. It is shown that the suppression of T
c by doping originates largely from structural changes and the structure properties play an important role in influencing the
normal-superconductor transport. The introduction of defects into the Mg layers and other aluminum compound (Al2O3, MgAlB4) impurity phases both influence the polycrystalline structure. 相似文献
7.
A. T. M. K. Jamil H. Noguchi K. Shiratori T. Kondo H. Munekata 《Journal of Superconductivity and Novel Magnetism》2005,18(3):321-324
Ga–As–Fe composite films prepared by molecular beam epitaxy at 600°C on GaAs(100) substrates with the stacking sequence of
[100-nm GaAs/50-nm Fe3Ga2−
x
As
x
/100-nm GaAs] exhibit the distinct photo-enhanced magnetization at room temperature. Transmission electron microscopy reveals
the formation of metamagnetic Fe3Ga4 grains on the sample surface. Illumination power dependence of the enhanced magnetization has been carefully compared with
the antiferromagnetic-type magnetization–temperature (M–T) curve (Neel temperature of T
N = 340–390 K), from which we have discussed the existence of photon-mode photo-enhanced magnetization of some sort in addition
with the enhancement due to the light-induced heating. 相似文献
8.
The behavior of the superconducting transition temperature T
c
and that of the jump of electron heat capacity (C
S
−C
N
)/C
N
of the compound MgB2 at T=T
c
with substitution of boron and magnesium atoms by other atoms from the periodic table of the elements, corresponding to introduction
of additional electrons or holes in this compound are researched. The microscopic superconductivity theory in MgB2 systems in the magnetic field parallel to the crystallographic axis (H
‖
c) is built. The magnitude of the upper critical field H
c2 is determined and its temperature dependence in two-band systems with different and identical topologies of Fermi surface
cavities of the corresponding bands is studied. The obtained results and their comparisons with the experimental data demonstrate
that all kinds of anomalies of the physical properties of the compound MgB2 are effectively described by the two-band model. 相似文献
9.
The present paper focuses on methods of further improving the flux pinning and critical current density of disk-shaped MgB2 bulk superconductors by adding excess Mg metal in combination with an optimum silver content and optimized processing conditions. Bulk MgB2 samples were produced by in situ solid-state reaction in Ar gas ambient using high purity commercial powders of Mg metal and 1.5 wt% carbon-coated amorphous B powders mixed in a fixed ratio of Mg/B = 1.1:2. Further, 4 wt% silver was added to improve flux pinning as well as mechanical performance of the bulk MgB2 material. The magnetization measurements confirmed a sharp superconducting transition with Tc,onset at around 37 K, which is only by 1 K lower than in bulk MgB2 material produced without carbon-coated amorphous boron. The critical current density (Jc) values significantly improved in the MgB2 material with 4 wt% of silver and 1.5 wt% of carbon-coated amorphous boron, sintered at 775 °C for 3 h. At 20 K, this sample showed Jc at around 500 and 350 kA/cm2 in the self-field and 1 T, respectively, which makes it suitable for several industrial applications. 相似文献
10.
A complex perovskite oxide, YbBa2NbO6, as a non-reacting substrate for YBa2Cu3O7-° super-conducting film has been developed. The dielectric constant and loss factor values of the material are in the range
suitable for its use as substrate for microwave applications. A YBa2Cu3O7−δ superconducting thick film dip coated on YbBa2NbO6 substrate gave a Tc (0) of 92 K and current density of ∼ 1.3 × 104 A cm−2. 相似文献
11.
Semiconducting glasses of the Fe2O3-Bi2O3-K2B4O7 system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (Tg) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe2O3 content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility. 相似文献
12.
S. Balamurugan 《Journal of Superconductivity and Novel Magnetism》2011,24(5):1633-1641
The impact of slightly tuning molar ratio in the starting materials on the physical properties of 1212-type rutheno-cuprate, YSr2Ru0.9Cu2.1O7.9 (nominal) samples prepared under four synthesis approaches are reported. Interestingly, all samples clearly show the differences
in the physical properties of the samples prepared under different synthetic protocols. However, neither XRD nor EDX reveal
any notable differences in the crystal structure or sample composition. All the samples exhibit magneto-superconducting properties (H
ext=5 Oe) which are slightly varied with synthetic approaches. The high field (H
ext=10 kOe) temperature dependence of magnetization data shows a sharp ferromagnetic transition around 150 K and all the samples
obey Curie–Weiss linear behavior above 180 K. The experimental effective paramagnetic moment for the various samples is in
the range of 2.5 and 2.7μ
B/Ru which are in line with the literature report. The magnetization, M(H) isotherm curves measured at 5 K and −10 kOe≤H≤10 kOe conditions reveal weak ferromagnetic-like hysteresis loops for all samples with returning moment (M
r) and coercive field (H
c), whereas the high field M(H) loops indicate soft ferromagnetic behaviors with magnetic saturation. The saturation moment of the samples is slightly varied
with the synthesis approaches. None of the samples showed bulk superconductivity (TcR = 0)T_{\mathrm{c}}^{R = 0}) down to 2 K, while all samples show onset transitions (TconsetT_{\mathrm{c}}^{\mathrm{onset}}) except the sample prepared by approach-3. The latter approach sample shows semiconducting behavior down to 2 K. The TconsetT_{\mathrm{c}}^{\mathrm{onset}} noticed at 34 K, 12 K, and 6 K for the sample prepared by approach-1, 2, and 4, respectively. The nearly linear dependence
suggests that hopping conduction is dominant in certain temperature range for all samples. The magneto-transport features
of these samples exhibit maximum magnetoresistance (MR) at low temperatures. Remarkably, the sample prepared by approach-1 shows largest −MR about 77% at low temperature 2 K and H=90 kOe which stimulates for further investigations. Among the four synthesis approaches employed in the present study, we can probably suggest that the approach-1 (0.5Y2O3+0.5SrO2+1.5SrCuO2+0.9RuO2+0.6CuO) is the preferable method to achieve the best sample (in terms of magneto-transport features). 相似文献
13.
This study reports the effect of coronene (C24H12) addition on some superconducting properties such as critical temperature (Tc), critical current density (Jc), flux pinning force density (Fp), irreversibility field (Hirr), upper critical magnetic field (Hc2), and activation energy (U0), of bulk MgB2 superconductor by means of magnetisation and magnetoresistivity measurements. Disk-shaped polycrystalline MgB2 samples with varying C24H12 contents of 0, 2, 4, 6, 8, 10 wt%, were produced at 850 °C in Ar atmosphere. The obtained results show an increase in field-Jc values at 10 and 20 K resulting from the strengthened flux pinning, and a decrease in critical temperature (Tc) because of C substitution into MgB2 lattice, with increasing amount of C24H12 powder. The Hc2(0) and Hirr(0) values are respectively found as 144, 181, 172 kOe, and 128, 161, 145 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. The U0 depending on the magnetic field curves were plotted using thermally activated flux flow model. The maximum U0 values are respectively obtained as 0.20, 0.23 and 0.12 eV at 30 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. As a result, the superconducting properties of bulk MgB2 at high fields was improved using C24H12, active carbon source addition, because of the presence of uniformly dispersed C particles with nanometer order of magnitude, and acting as effective pinning centres in MgB2 structure. 相似文献
14.
E. Yucel Cabir Terzioglu A. Varilci I. Belenli 《Journal of Materials Science: Materials in Electronics》2011,22(8):1143-1153
We have fabricated MgB2/Fe monofilament wires and tapes by a powder-in tube (PIT) technique, using an ex-situ process without any intermediate annealing.
MgB2/Fe monofilament tapes were annealed at 650–1,050°C for 60 min and 950°C for 30–240 min. We have investigated the effect of
annealing temperatures and times on the formation of MgB2 phase, activation energy, temperature dependence of irreversibility field H
irr(T) and upper critical field H
c2(T), transition temperature (T
c), lattice parameters (a and c), full width at half maximum, crystallinity, resistivity, residual resistivity ratio, active cross-sectional area fraction
and critical current densities. We observed that the activation energies of the MgB2/Fe monofilament samples increased with increasing annealing temperature up to 950°C and with increasing annealing time up
to 60 min while it decreased with increasing magnetic field. For the MgB2/Fe monofilament tape, the slope of the H
c2–T and H
irr–T curves decreased with increasing annealing temperature from 850 to 950°C as well as with increasing annealing time from 30
to 60 min. The transport and microstructure investigations show that T
c, J
c and microstructure properties are remarkably enhanced with increasing annealing temperature. The highest value of critical
current density is obtained for the sample annealed at 950°C for 60 min. The J
c and T
coffset values of the sample annealed at 950°C for 60 min were found to be 260.43 A/cm2 at 20 and 38.1 K, respectively. 相似文献
15.
Shufang Wang Wei Yu Guangsheng Fu 《Journal of Superconductivity and Novel Magnetism》2008,21(7):427-430
This paper presents a very simple way to synthesis MgB2 thick films with high critical current density in a magnetic field by ex-situ annealing precursor B films in air with excessive Mg in a sealed quartz tube. The films show a significant improvement of
critical current density in a magnetic field compared to the high purity films annealed in vacuum, while its zero-resistance
transition temperature T
c
zero and normal state resistivity still maintain about 38 K and 17 μΩcm. The results demonstrate MgB2 thick films have great potential applications in superconducting coated conductors.
相似文献
16.
Shuo Tao Yongbo Li Guowei Chen Xiaopeng Zhao 《Journal of Superconductivity and Novel Magnetism》2017,30(6):1405-1411
Enhancing the critical temperature (T C ) is important not only to widen the practical applications but also to expand the theories of superconductivity. Inspired by the meta-material structure, we designed a smart meta-superconductor consisting of MgB2 microparticles and Y2O3/Eu3+ nanorods. In the local electric field, Y2O3/Eu3+ nanorods generate an electroluminescence (EL) that can excite MgB2 particles, thereby improving the T C by strengthening the electron–phonon interaction. An MgB2-based superconductor doped with one of four dopants of different EL intensities was prepared by an ex situ process. Results showed that the T C of MgB2 doped with 2 wt% Y2O3, which is not an EL material, is 33.1 K. However, replacing Y2O3 with Y2O3/Eu3+II, which displays a strong EL intensity, can improve the T C by 2.8 to 35.9 K, which is even higher than that of pure MgB2. The significant increment in T C results from the EL exciting effect. Apart from EL intensity, the micromorphology and degree of dispersion of the dopants also affected the T C . This smart meta-superconductor provides a new method to increase T C . 相似文献
17.
Xue Wang Chen Guo Hu Yi Xi Chuan Hui Xia Xiao Shan He 《Journal of Superconductivity and Novel Magnetism》2010,23(6):909-911
Al-doped Fe3O4 nanoparticles were synthesized for the first time via the Composite-Hydroxide-Mediated (CHM) method from Fe3O4 and Al2O3 without using any capping agent. The synthesis technique was one-step and cost effective. The obtained products were characterized
by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS). Samples with a tunable
size of 500–1500 nm, 200–800 nm, and 100–700 nm could be obtained by adjusting the reaction time and temperature. Magnetic
property of the as-synthesized Al-doped Fe3O4 nanoparticles was investigated. Magnetic hysteresis loops measured in the field range of −10 kOe<H<10 kOe, indicated the ferromagnetic behavior with coercivity (H
c) of 470 and 110 Oe and remanence magnetization (M
r) of 13 and 6.4 emu/g at the temperature of 5 and 300 K, respectively. The saturation intensity (M
s) was 46.1 emu/g at 5 K, while it was about 43.6 emu/g at 300 K. 相似文献
18.
Caixuan Xu Anming Hu Naomichi Sakai Izumi Hirabayashi Mitsuru Izumi 《Journal of Superconductivity and Novel Magnetism》2007,20(4):309-314
Single domain GdBa2Cu7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed
Gd123 was successfully enhanced by addition of both BaCO3 and BaCuO2−x
, which suppress the formation of Gd1+x
Ba2−x
Cu3O7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO3 and 0.05 to 0.1, M BaCuO2−x
per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band
formed by Gd2BaCuO5 particle concentration appeared around the seeding zone in both a–b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and
8, mm in thickness and a high critical current density J
c up to 91,200, A/cm2 was achieved at 77, K under self-field. 相似文献
19.
A. V. Semeno A. A. Pronin N. E. Sluchanko N. A. Samarin A. V. Kuznetsov S. V. Demishev 《Journal of Superconductivity and Novel Magnetism》2007,20(2):109-112
Electron spin resonance of a single crystal of CuGeO3 doped with 2% of Co has been studied at f = 99 GHz in temperature range 1.8–50 K. Contributions to ESR absorption from Cu2+ chains and from Co2+ ions were derived. It is found that functions obtained for ESR integrated intensities: Curie-Weiss for Cu2+ (χCu ∼ C
Cu/(T + Θ), with Θ = 92 K) and Curie for Co2+ (χCo ∼ C
Co/T) are well consistent with temperature dependence of static magnetic susceptibility. Strong dependence of ESR absorption on
polarization of oscillating magnetic field was discovered for Co2+ contribution. Polarization effect was studied for magnetic field applied along a, b and c directions. Values of g-factors of resonance lines are presented. 相似文献
20.
M. Bleiweiss J. Amirzadeh M. Yin A. Lungu T. Datta 《Journal of Superconductivity and Novel Magnetism》2005,18(4):567-572
Synthesis and optical transmission of MgB2 thin films on optically transparent glass are reported. In the 400–1000 nm regime as deposited films show high metallic reflectivity
and very little transmission. After deposition, the films were annealedex situ and rendered superconducting withT
c of 38 K, approaching that of the bulk material. The reaction conditions where quite soft ∼ 10 min at 550°C. The optical absorption
coefficient,α and photon energy,E followed a Tauc-type behavior, (αE)1/2=β
T(E −E
g). The band gap (E
g) was observed to peak at 2.5 eV; but, the slope parameterβ
Tbehaved monotonically with reaction temperature. Our results indicate that an intermediate semiconducting phase is produced
before the formation of the superconducting phase; also optical measurements provide valuable information in monitoring the
synthesis of MgB2 from its metallic constituents. In addition these films have interesting optical properties that may be integrated into optoelectronics. 相似文献