共查询到20条相似文献,搜索用时 15 毫秒
1.
M. B. Solunke P. U. Sharma M . P. Pandya V. K. Lakhani K. B. Modi P. Venugopal Reddy S. S. Shah 《Pramana》2005,65(3):481-490
The compositional dependence of elastic properties of Al3+-substituted Bi(Pb)-2223 superconducting system with the general formula Bi1.7−x AlxPb0.3Sr2Ca2Cu3 Oy
(x = 0.0, 0.1, 0.2 and 0.3) have been studied by means of ultrasonic pulse transmission (UPT) technique at 1 MHz (300 K). The
elastic moduli of the specimens are computed and corrected to zero porosity. The observed variation of elastic constants with
aluminium substitution has been explained on the basis of the strength of interatomic bonding. The applicability of heterogeneous
metal mixture rule for estimating elastic constants and transition temperature has been tested. 相似文献
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E.M.M. Ibrahim 《Applied Physics A: Materials Science & Processing》2007,89(1):203-208
Polycrystalline samples of Zn0.37Mn0.58Fe2.05O4 have been prepared by the solid state reaction method. The structural characterization of the samples indicated that 1523 K
is the most proper temperature for obtaining a single phase spinel structure. The DC electrical conductivity measurement was
carried out by a two-probe method. Temperature dependent of DC electrical conductivity increases with increase in temperature
ensuring the semiconductor nature of the samples. The drift mobility was estimated and found to be temperature dependant.
The electrical conduction mechanism in these samples change from hopping, in the low temperature range, to polaron hopping
in the high temperature range. The portion of energy Δε anticipated in hopping was determined. It decreases with increasing
the sintering time and temperature.
PACS 70; 71.20.Nr; 75.50.Gg 相似文献
3.
Summary Monofilamentary Bi(2223) tapes withJ
c(77 K, 0 tesla) up to 30 000 A/cm2 have been prepared by cold rolling using the powder-in-tube method. An optimization of the precursor powders has led to a
higher phase purity after the reaction heat treatment. The deformation process has been optimized in order to increase the
oxide density and to reduce sausaging effects on the oxide thickness. The transport properties of these tapes have been studied
in a wide range of temperature (4.2K-T
c) and magnetic fields (up to 28 tesla). The critical-current values at 77 K fields of 0.5 T and 1 T parallel to the tape surface
are 10 000 A/cm2 and 5400 A/cm2, respectively. At 4.2 K theJ
c value decreases from 1.6·105 A/cm2 at 0 T to 6·104 A/cm2 at 15 T. At fields higher than 15 tesla a very low field dependence ofJ
c has been found, regardless of the tape orientation. Transport properties have also been studied by cutting small sections
of the tape in order to investigate the local critical-current distribution. It has been found that, even in rolled tapes
of good quality (J
c (77 K, 0 T)>20000 A/cm2), theJ
c distribution is homogeneous: the critical current density increases gradually from the centre of the tape to the sides, the
latter exhibiting much higherJ
c (46000 A/cm2) than in the centre (18000 A/cm2).
Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994. 相似文献
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Both the oxygen content and Tonset c of the Bi2Ca2.5(Ln, Ln+)0.5Cu2O y system monotonically increases as the mean ionic radius of (Ln, Ln+) increases. The structural modulations in all of the samples are almost commensurate with a period equal to 9b. In Bi2-xPbCa2.5Nd0.5Cu2O y , Tonset c decreases with increasing Pb concentration. In order to investigate the effect of post annealing using a hot isostatic press (HIP), Bi2Ca2.5La0.25Pr0.25Cu2O y was processed under different HIP conditions. This result suggested that HIP annealing causes a phase change from the 232 structure to the 221 structure. 相似文献
6.
《Journal of magnetism and magnetic materials》2001,237(1):22-26
Low-field AC susceptibility measurements have been made, at different values of AC field amplitude Hm (26–600 A/m), on Eu:123 and Bi:2223 samples. Analysis of the temperature dependence of the AC susceptibility has been done employing Beans’ critical state model. The intergranular critical current density (Jc) is calculated as a function of both Hm and temperature for both samples, respectively. It is found that Jc increases with increasing Hm for both samples and its values are generally higher in Bi sample than in Eu sample. Our results are discussed in terms of zero-temperature pinning potential βI(0) in both systems. 相似文献
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A. Amira A. Saoudel Y. Boudjadja L. Amirouche N. Mahamdioua A. Varilci M. Akdogan C. Terzioglu M.F. Mosbah 《Physica C: Superconductivity and its Applications》2011,471(23-24):1621-1626
Superconducting ceramics of Bi1.6Pb0.4Sr2Ca2Cu3OyFx (x = 0–0.6) are prepared in air by conventional solid state reaction and characterized. The study shows that the melting point of the samples decreases as fluorine content increases. As a consequence, the grain size increases with the doping level and for x = 0.6, the sample is completely deformed and presents a concave shape making impossible the measurements on it. The Vickers microhardness reaches its maximum for x = 0.2. The analysis of the X-ray diffraction results reveals that all the samples are composed of only Bi(Pb)-2212 and Bi(Pb)-2223 phases. The highest proportion of the high Tc phase (Bi(Pb)-2223) is also observed for x = 0.2 and is about 67.32%. The refinement of cell parameters is done by considering the structural modulation. The results show that the doping leads to a reduction of cell volume as well as the a axis component of modulation. From resistivity versus temperature measurements, it is shown that the doped phases exhibit higher onset critical transition temperatures than the undoped one. The residual resistivity increases with fluorine content suggesting that the doping introduces structural defects and disorder into the samples. The obtained critical current density at 77 K under zero magnetic field also increases with fluorine doping. 相似文献
12.
M. Iwakuma Y. Tajika K. Kajikawa K. Funaki T. Matsushita E. S. Otabe N. Ayai K. Hayashi K. Sato 《Physica C: Superconductivity and its Applications》1998,310(1-4):154-158
We fabricated Bi2223 multifilamentary sample wires with various twist pitches and investigated the electromagnetic properties experimentally. They showed monofilamentlike electromagnetic properties regardless of twisting due to the contacts among filaments and/or proximity effect. The observed AC losses in the non-twisted sample wire agreed roughly with the theoretical prediction for a homogeneous superconducting slab with the same thickness of the filamentary region on the basis of Irie–Yamafuji model. However the AC losses in the twisted wires deviated from the theoretical ones, especially for the amplitude around the theoretically predicted penetration field of the slab. We showed that the observed AC loss properties can be explained by both the twist effect for the macroscopic shielding current and the contribution of the local shielding current. 相似文献
13.
E. Braun W. Schnelle H. Broicher J. Harnischmacher D. Wohlleben C. Allgeier W. Reith J. S. Schilling J. Bock E. Preisler G. J. Vogt 《Zeitschrift für Physik B Condensed Matter》1991,84(3):333-341
We present measurements of the specific heat and of the thermal expansion of the most prominent phases of the Bi and Tl high temperature superconductors (Bi-2212, Bi-2223, Tl-2212, Tl-2223) in the neighbourhood ofT
c
. In all these systems we observe small but sharp anomalies which have very little similarity with the mean field jump found in the conventional superconductors. The analysis of these anomalies shows clear evidence for the presence of strong fluctuations of the order parameter. For temperatures more than 5 K away fromT
c
,2D Gaussian fluctuations are found, while within ±5 K ofT
c
the fluctuation contribution is best fitted by critical fluctuations. The shape of the thermal expansion anomalies is similar to that of the specific heat. Combination of both measurements predicts dT
c
/dp+0.2 K/kbar for Bi- and Tl-2223 systems. 相似文献
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We extend the study of a model for layered high-temperature superconductors to finite temperatures. The model assumes Fermi liquid properties for the carriers, which form a narrow tight-binding band. The carriers are subject to on-site intralayer and nearest neighbor interlayer interactions. The previous studies of the zero temperature properties, revealing remarkable agreement with experimental data, are extended to finite temperatures. These properties include the tunneling conductance for diffuse and specular transmission in a normal isolator superconductor junction, specific heat, nuclear spin relaxation time and the London penetration depth. Our results are compared with experimental findings. 相似文献
17.
《Physica C: Superconductivity and its Applications》1999,311(1-2):65-74
Nanometer SiC particles were added to (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) precursor powders and the powders were transformed into silver-sheathed superconducting tapes by the standard powder-in-tube (PIT) technique. The influence of SiC on the melting temperature, high-Tc (Bi2223) phase formation, microstructure and transport property of the tapes was studied by means of DTA, XRD, SEM/EDX, electrical and magnetic measurements. The results showed that SiC addition lowered the melting temperature of the superconductor powders and consequently, decreased the optimum sintering temperature of the tapes. However, the addition did not affect the Bi2223 phase formation and critical temperature (Tc) of the tapes up to 1.00 wt.% of SiC. Most importantly, the addition of a small amount of SiC (0.15 wt.%) improved the critical current (Ic) and Ic behavior in magnetic field as a result of the enhancement in density, grain alignment, grain connectivity and flux pinning of the tapes. 相似文献
18.
利用脉冲回波重迭方法,测定了新型高温超导陶瓷Bi1.7Ph0.3Sr2Ca2Cu3O10+x及Bi1.7Pb0.3Sr2CaCu2O8+x单相多晶样品的超声声速,并进而决定了其弹性常数。在200K附近,横波和纵波声速均出现反常突变,并伴随有衰减峰出现,表明存在某种结构变化或相变,与此同时还出现了显著的模量软化,由声速导出的Bi系各弹性模量值远小于YBa2Cu3O7-y超导体及BaTiO3等具有类似结构陶瓷的相应值,而它们的泊松比却十分相近,表明这几种钙钛矿结构陶瓷有着类似的原子间结合力;而当C轴变长,其层间耦合减弱。在考虑空洞影响并加以修正后,得到材料的德拜温度为270±20K,并进而首次得到该材料的德拜温度随温度变化的曲线。 相似文献
19.
Bi2 2 2 3银包套超导带材是研制高温超导磁体和高温超导强电应用的基础。文中就对高温超导磁体最大运行电流有重要影响的 Bi2 2 2 3银包套带材侧向弯曲形变进行了初步探讨 ,就不同的侧向弯曲率对超导带载流能力的影响进行了实验测试 ,并提出了提高 HTS磁体最大运行电流的方法。 相似文献
20.
测量了77K温度下不同基体材料和不同芯数带材的临界电流和交流损耗.分析了弯曲应变对它们的影响.结果表明单芯样品的不可逆应变小于0.15%,而多芯样品的不可逆应变在01%到03%之间,多芯导体的机械性能比单芯导体的好,增加芯数可以提高机械性能,金属包套材料对超导芯起到了增强的作用,它防止了超导芯中裂纹的进一步传播.自场损耗随外加应变的增加而增加,这种大幅度的增加与应变使带材的临界电流急剧减小直接相关
关键词:
高温超导体
临界电流
交流损耗 相似文献