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1.
Abstract A number of Nb3Ge samples with rather high T c,on (T c,on ? 22.5 K) were prepared by CVD and characterized by the electrical resistance, X-ray diffraction and scanning electron microscope patterns. It was found that the crystal growth patterns are roughly divided into two categories, (i) a particles-pattern in a nearly single phase of Nb3Ge and (ii) a network pattern with a fairly large amount of the Nb5Ge3 phase but with rather a large resistance ratio and a small resistivity at T ? T c,on. The latter type of samples shows generally higher T c,on. It is deduced that the origin of high T c,on comes mainly from a deformation of the atomic potential at the Nb-site into an anharmonic and rather unstable shape due to the coexistence of the Nb5Ge3 phase. The mechanism of the formation of different patterns is discussed on the basis of the theory of non-equilibrium thermodynamics of Prigogine. 相似文献
2.
Jiří Růžička 《Zeitschrift für Physik A Hadrons and Nuclei》1970,237(5):432-441
Superconducting samples of the nominal composition Nb x (Al1?y , Ge y )1?x withx reaching from 0.72 to 0.78 andy from 0.175 to 0.30 were prepared and the superconducting transitions of as-cast and of annealed samples were measured. The onset of superconductivity for samples with a suitable composition and annealing procedure has been observed to be at about 21.05 K. By the help of anodic oxydation process and by multichannel semiconductor x-ray spectroscopy with scanning electron microscope it has been possible to carry out the phases distribution and detailed phase-analysis in the samples. 相似文献
3.
Current and conductance characteristics have been obtained for Nb3(Al0.75Ge0.25)-barrier-Pb0.7Bi0.3 superconducting tunneling junctions prepared on Nb3(Al0.75Ge0.25) ribbon substrates. Thermal oxide, anodized, and amorphous carbon tunneling barriers were used. These junctions are relatively fragile: they deteriorate under temperature recycling or sustained bias. Typical junction resistances are of the order of 50Ω, and 2Δ(0) of Nb3(Al0.75Ge0.25) is ~1.3 meV. 相似文献
4.
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
5.
The unsuitable mechanical properties of Nb3Sn (its brittleness) make the production of a conductor in the required shape and dimensions very difficult. A method has been proposed and experimentally investigated by which the existing superconducting Nb3Sn tape could be modified to obtain intrinsically stable superconductor. The required filamentation of commercial Nb3Sn conductor is manageable by electron-beam microetching. The achieved results could serve as a starting point for the construction of a special electron-beam machine. Such device may work in connection with the Nb3Sn producing apparatus.The authors are grateful to I.Hlásnik for the encouraging discussions, to V.ernuko for providing us with the Nb3Sn vapour deposited tape and to S.Koina for performing the microanalysis. 相似文献
6.
H. Utsunomiya T. Sakai Y. Saito T. Matsuo 《Physica C: Superconductivity and its Applications》1995,250(3-4):340-348
Silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox (Bi(2223)) tapes were fabricated by the “oxide-powder-in-tube” technique. After the tapes were shaped and sintered, an additional cold rolling and a re-sintering were applied in order to enhance the critical current density Jc. The influence of the additional rolling conditions (roll diameter, number of passes, lubrication) on the Jc (77 K, 0 T) was made clear. The influence of the sintering conditions (temperature, heating rate) on Jc was also investigated. As for the rolling conditions, a small redundant shear deformation or a small contact angle leads to a good grain alignment, texturing, and a higher Jc value. As for the temperature of the first sintering, 1113 K is superior to 1118 K because of the volume fraction of the Bi(2223) phase. 相似文献
7.
Results concerning the pinning behaviour of thin Nb3Ge films prepared by sputtering and evaporation onto hot sapphire substrates are reported. The validity of scaling laws in the range of magnetic fields up to 13 T has been verified. We have found that the pinning dependence in evaporated films obeys these laws, however, the maximum of the volume pinning force occurs at constant magnetic field value for sputtered Nb3Ge films. A different microstructure of these two types of films is made responsible for the anomalous pinning behaviour described. 相似文献
8.
Brandon Wilfong Muhtar Ahart Stephen A. Gramsch Chris Stock Xiaomin Li H. Luo Russell J. Hemley 《Journal of Raman spectroscopy : JRS》2016,47(2):227-232
The vibrational and structural properties of Pb(Fe0.5Nb0.5)O3 have been investigated using Raman spectroscopy up to 40 GPa at 300 K and from 300 to 415 K at selected pressures. The measurements reveal three phase transitions, at 5.5, 8.7, and 24 GPa at room temperature. The temperature dependences of the spectra indicate transitions at 1.5 GPa, at 335 and 365 K. The results are consistent with the appearance of an intermediate tetragonal P4mm phase between the ferroelectric R3m and paraelectric Pm‐3m phases. A P–T phase diagram is proposed that allows further insight into the magnetoelectric coupling present in this material. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
9.
Very low hysteretic losses have been measured in CVD prepared Nb3Ge. An apparent correlation between second phase content and low losses has been found as well as a reduction in hysteretic loss by appropriate surface treatment. 相似文献
10.
We have used the tight-binding method to calculate the local densities of states of unreconstructed Ge (111) and GaAs (111), () surfaces. In the unrelaxed surface configuration we find two types of states for each surface. The effects of relaxation on Ge surface states are also discussed. 相似文献
11.
Brihuega I Custance O Ugeda MM Oyabu N Morita S Gómez-Rodríguez JM 《Physical review letters》2005,95(20):206102
We have investigated the recently reported structural phase transition at low temperature (LT) for alpha-Pb/Ge(111) [from a (3 x 3) symmetry to a disordered phase] using scanning tunneling microscopy (STM). By tracking exactly the same surface regions with atomic resolution while varying the sample temperature from 40 to 140 K, we have observed that substitutional point defects are not mobile, in clear contrast to previous assumptions. Moreover, STM data measured at the lowest temperatures ever reported for this system (10 K) show that while filled-state images display the apparent signature of a glassy phase with no long-range order, in empty-state images honeycomb patterns with (3 x 3) periodicity, and not distinguishable from data measured at much higher temperatures, are clearly resolved. These new observations cast serious doubts on the nature and/or on the existence of a disordered phase at LT. 相似文献
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13.
采用脉冲激光沉积(PLD)镀膜技术在倾斜10°的LaAlO3(100)单晶衬底上制备了(SrTiO3)n/(SrTi0.8Nb0.2O3)m系列超晶格.在超晶格薄膜的XRD图谱中清楚地观察到周期调制的卫星峰结构.从卫星峰的分布计算了超周期,进而得到了在生长SrTiO3和SrTi0.8Nb0.2O3时的沉积速率,分别为0.78 /pulse和0.57 /pulse.在超晶格薄膜中发现了激光感生热电电压(LITV)效应,说明这种人造原子层热电堆结构具有Seebeck系数各向异性.研究发现,在SrTiO3介电层厚度n=46.8 nm,SrTi0.8Nb0.2O3导电层厚度m=19.0 nm时LITV信号的平均峰值电压最大U -P=0.7 V/mJ·mm,n=46.8 nm,m=11.4 nm时LITV信号的平均响应时间最小τ -=124 ns. 相似文献
14.
G. N. Mikhailova E. I. Demikhov V. P. Aksenov L. Kh. Antonova L. D. Iskhakova L. N. Zherikhina E. A. Kostrov S. V. Lavrishchev V. S. Mikhailov A. V. Troitskii A. M. Tskhovrebov 《Technical Physics》2009,54(2):235-238
The stability of critical parameters T c and I c of commercial high-temperature superconducting wires upon long-term passage of transport current (about 0.7I c) in liquid nitrogen (77 K) is studied. Voltage-current characteristics U(I), as well as the critical current and critical temperature, are investigated for the case of Bi(2223) hermetic multifilament wires and Dy(123) superconducting tapes covered by a thin Ag layer. In the former case, a considerable decrease in the critical current (by ~30%) and swelling of the wires after passage of the current for 323 h are observed. The same is true for a reference sample, which does not experience the action of current and stays in liquid nitrogen for 700 h. The decrease in the critical current in the Bi(2223) sample is likely to be associated with penetration of a liquid coolant into the composite conductor: evaporating and expanding as a result of heating, it severely deforms the material. The Dy(123) sample grown epitaxially demonstrates high stability of the critical current after it has experienced the action of current for 400 h and been kept in liquid nitrogen for 1000 h. 相似文献
15.
K. Vavřina 《Czechoslovak Journal of Physics》1971,21(3):275-284
The paper describes measurements of the current-voltage characteristic of polycrystalline selenium layers at high current density values. At first it is shown that the composition of a counter electrode (Sn, Cd, CdSn) does not influence the character of the dependence of the current density vs. voltage. When measuring the influence of thickness of polycrystalline layers of selenium on the behaviour of the current-voltage characteristic, three regions on the current-voltage characteristic were observed. For the lowest voltage the current density isjU/d and so Ohm's law can be used. For higher voltagejU1.35/d1.175. For the highest voltage the relationjU
2/d1.5 was found. It will probably be possible to explain the results of measurements by means of the existence of space-charge-limited current.I should like to express my sincere gratitude to the specialists from the Institute of the Rectifiers Research at B~chovice for their very careful preparation of the samples, which made possible to carry out really reproducible and comparable measurements. 相似文献
16.
Zhang S Zhao YG Li PS Yang JJ Rizwan S Zhang JX Seidel J Qu TL Yang YJ Luo ZL He Q Zou T Chen QP Wang JW Yang LF Sun Y Wu YZ Xiao X Jin XF Huang J Gao C Han XF Ramesh R 《Physical review letters》2012,108(13):137203
We report a large and nonvolatile bipolar-electric-field-controlled magnetization at room temperature in a Co(40)Fe(40)B(20)/Pb(Mg(1/3)Nb(2/3))(0.7)Ti(0.3)O(3) structure, which exhibits an electric-field-controlled looplike magnetization. Investigations on the ferroelectric domains and crystal structures with in situ electric fields reveal that the effect is related to the combined action of 109° ferroelastic domain switching and the absence of magnetocrystalline anisotropy in Co(40)Fe(40)B(20). This work provides a route to realize large and nonvolatile magnetoelectric coupling at room temperature and is significant for applications. 相似文献
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F. Smend W. Weirauch W. -D. Schmidt-Ott A. Flammersfeld 《Zeitschrift für Physik A Hadrons and Nuclei》1967,207(1):28-34
Absolute cross-sections and isomeric cross-section ratios have been measured for the reactions89Y(α, 3n)90g, 90m Nb. The energy of the α-particles was varied between 34 and 54 MeV. The experimental isomeric ratios are compared with statistical-model calculations. 相似文献
20.