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Amorphous YNi2B2C powders have been produced by mechanical attrition. Superconductivity is absent in the amorphous state but recovers upon crystallization. However, the superconducting transition temperature TC is lower than that of the melted analogue. TC can be increased by increasing the annealing temperature. High temperature compaction leads to dense bulk superconducting samples. TC of these bulk samples can be optimised by annealing. Variations in TC are attributed to deviations from stoichiometry. Contamination of the powders with WC wear debris upon annealing may deteriorate the superconducting properties. 相似文献
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Y. S. Wang P. Bennema L. W. M. Schreurs C. J. Beers J. Wunk P. Van Der Linden 《Crystal Research and Technology》1993,28(2):253-256
In this paper we present the results of recent studies on the improvement of superconductivity in PbxBi2-xSr2CaCu2Oy single crystals by preventing impurities incorporation, employing ZrO2 crucible for crystal growth and post annealing the as-grown crystals in vacuum or argon. It is realized that the superconductivity of as-grown crystals is improved. 相似文献
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Kenji Sakamaki Hiroaki Wada Hiroshi Nozaki Yoshichika Onuki Maki Kawai 《Molecular Crystals and Liquid Crystals》2013,570(2):99-104
Abstract Evidence for bulk superconductivity in Nb2SC0.90 carbosulfide is presented. Diamagnetic volume fraction of Nb2SC0.90 was precisely determined with low applied magnetic fields which were corrected by 6N lead rod as an internal standard. Based on magnetic field dependence of magnetic moment at several constant temperature's below TC = 5 K, Nb2SC0.90 is found to be a type II superconductor with relatively high H C2 and low HC1. 相似文献
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The polytypoidic structures in the Bi-system of superconductors characterized by X-ray, electron diffraction and TEM technique are described. A strong incommensurate modulated diffraction was observed by these methods in the 2223-phase. In addition, we revealed the Laue streaks for the one-dimensional disorder, the banded structure perpendicular to the c-axis. We suppose that the intergrowth is an indication of the displacement in the Bi-O layers. It is evident that the polytypoidic concept allows us to describe the structure and physical properties of these superconducting phases in a unified manner. So it is shown that the polytypoidism is a general feature of the Bi-system materials. 相似文献
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K. Bechgaard K. Carneiro O. Eg M. Olsen F. B. Rasmussen C. Jacobsen 《Molecular Crystals and Liquid Crystals》2013,570(1):627-632
The organic charge transfer salt di-tetramethyl-tetraselenafulvalenium perchlorate becomes superconducting with transition temperatures from 0.9-1.4 kelvin. We compare our results to those of other groups and discuss possible reasons for the observed differences. Preliminary results are given for an alloy with the corresponding perrhenate. 相似文献
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S.S.P. Parkin F. Creuzet M. Ribault D. Jérome K. Bechgaard J. M. Fabre 《Molecular Crystals and Liquid Crystals》2013,570(1):605-615
Abstract We report pressure dependent studies of the a-axis resistivity as a function of temperature for several members of the isostructural families of organic charge transfer salts, (TMTSF)2X and (TMTTF) 2X. For a typical (TMTSF)2X material the low temperature metal-insulator transition seen at 1 bar is suppressed above some critical pressure, Pc, where a superconducting transition is observed near 1 K. We find a correlation between Pc and the ambient pressure c lattice parameter which reflects the anion size. The (TMTTF) cX salts exhibit very different ambient pressure behaviour but we find that with the application of sufficiently high pressures (~30 kbar) their behaviour resembles that seen in the (TMTSF)2X family but at lower pressures. In particular we find evidence of a possible superconducting transition near 4 K in (TMTTF)2Br at 25 kbar. At this pressure the conductivity near 4 K is extremely high with a value approaching 106 (Ωcm)?1 and the resistivity ratio is about 400. 相似文献
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A. Fournel C. More G. Roger J. P. Sorbier J. M. Delrieu D. Jerome 《Molecular Crystals and Liquid Crystals》2013,570(1):617-626
Electron tunnelling data in (TMTSF)2 X-GaSb Schottky barriers support the idea that strong superconducting fluctuations exist in quasi-one-dimensional (TMTSF)2X up to temperatures which are about one order or magnitude higher than the 3-D ordering critical temperature. Other tunnelling data tend to indicate that stabilization of superconductivity is possible at high temperature via chain cross-linking. 相似文献
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A theory for the coexistence problem of the spin density wave (SDW) and superconductivity (SC) in highly anisotropic materials is presented. On the basis of a simplified electronic band model a Hartree-Fock approximation is applied. It is concluded that SDW is precluded when SC developes at a higher temperature. When the SDW onset temperature is higher than that of SC, these long range orders generally coexist unless two orders interchange by a first order phase transition. Discussions on possible phase diagrams for (TMTSF)2PF6 under pressure are given. 相似文献
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Crystallography Reports - A film of high-temperature superconductor (HTSC) YBa2Cu3O7 has been grown on the (100) crystallographic plane of SrLaGaO4 crystal using pulse laser deposition. An... 相似文献
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采用传统的固相反应法在较低的烧结温度与较短的煅烧时间下制备了(La1.85Sr0.15CuO4)1-x(La2/3 Sr1/3MnO3)x(简写为LSCO/LSMO)超导/铁磁复合材料.结果显示:复合后LSMO中的结构没有发生明显改变,随着温度的降低,所有的复合材料在38 K左右均会出现电阻急剧下降,最终呈现超导现象.甚至当LSMO铁磁性材料掺入达到O.20mol时,复合材料仍旧呈现超导态.同时所有复合样品的超导转变温度TC随着x的增加呈现线性下降的趋势.因此,通过低温与短时的烧结方法可以避免处于晶界处的LSCO的CuO面被破坏,进而提高超导/铁磁复合材料中在晶界处的铁磁的共存含量. 相似文献
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The relation between the phase transition temperature and unit cell volume in the (K1-xCsx)2ZnCl4 mixed crystals was studied. The phase transition temperature of A2BX4 family is dependent on the size of cation and anion (FABRY and PEREZ-MATO). That is, the transition temperature of crystal decreases with increasing unit cell volume. In this study we investigated this property of mixed crystals with the increasing mixture ratio. From the current study, we obtained the result that in the mixed crystals (K1-xCsx)2ZnCl4, the increase of x induces the increase of unit cell volume, so that TI decreases with increasing unit cell volume. In order to determine the distribution of the substituted Cs+, using the near IR and UV spectrophotometer, we investigated both the band gap energy and the type of transition. 相似文献
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采用水热法改变NaOH体积制备了不同形貌的CaTi2O4(OH)2粉体,利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)对样品进行了微观结构分析,并利用紫外-可见吸收测试仪对样品的吸收边进行了测试与分析.研究不同NaOH体积对CaTi2O4(OH)2片状结构的发育与生长、产率和光催化性能的影响.结果表明:随着NaOH体积的增加,有利于CaTi2O4(OH)2片状结构的发育与生长,并在(040)、(251)、(371)晶面上具有择优生长的习性,使得CaTi2O4(OH)2产率可达到94.2;.然而,所制备样品的光吸收与光催化性能却随着NaOH体积的增加反而降低.当加入2.4 mL NaOH所制备样品在紫外可见光下120 min对罗丹明B的分解率达到93.7;. 相似文献
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G. A. Gumanski V. V. Chodasewitsch O. Brümmer N. Wagner 《Crystal Research and Technology》1979,14(5):581-588
Polycristalline Ni samples were bombarded by 30 keV Ar ions with dose rates from 1016 ions/cm2 to 1017 ions/cm2. The investigation of the electronic states 1 S1/2O, 1 S1/2C and 2 P3/2Ni was made by X-ray photoemission spectroscopy (XPS). The XPS core level spectra show features refering to different chemical compounds of oxygen and carbon with nickel. We have studied the change of this spectrum structure dependent on distance of the sample surface for various doses of implantation. 相似文献
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Gustavo Avila Luis Angel Maldonado Rubén A. Toscano 《Journal of chemical crystallography》1997,27(2):125-128
The cyclobutane ring displays a puckered conformation with the amide group in a perpendicular conformation. An intramolecular
hydrogen bond held fixed the orientation of the 2-hydroxy-2-propyl moiety, causing the magnetic non equivalence of methyl
groups observed in the room temperature1H-NMR spectrum. Crystal packing reveals the formation of bi-molecular layers parallel to thebc plane. The compound crystallizes in the space groupP21,/c witha=13.351(3),b=7.569(2),c=13.271(3)Å and β=92.03(3)o.
Contribution No. 1549 of Instituto de Química, UNAM. 相似文献
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The crystal structures of 1-acetoxy-1-cyano-2-naphthylethylene (I) and 1,1-dicyano-2-naphthylethylene (II) are determined by X-ray structure analysis. Crystals I are monoclinic; at 25° C, the unit cell parameters are as follows: a = 17.308(6) Å, b = 4.507(1) Å, c = 17.845(5) Å, β = 107.90(2)°, V = 1324.7(7) Å3, d calcd = 1.260 g/cm3, Z = 4, and space group P21/n. Crystals II are monoclinic; at 25°C, the unit cell parameters are a = 3.827(1) Å, b = 15.784(4) Å, c = 17.226(2) Å, β = 91.22(2)°, V = 1040.3(4) Å3, d calcd = 1.304 g/cm3, Z = 4, and space group P21/n. It is revealed that, in crystal structures of I and II, the molecular stacks characteristic of compounds of this series are formed through stacking contacts along the direction of the smallest lattice parameter. 相似文献
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I. P. Raevskii V. V. Eremkin V. G. Smotrakov M. A. Malitskaya S. A. Bogatina L. A. Shilkina 《Crystallography Reports》2002,47(6):1007-1011
Single crystals of the composition PbFe1/2Ta1/2O3 are grown by the method of mass crystallization from flux. It is established that, unlike the PbFe1/2Ta1/2O3 ceramic, the synthesized single crystals possess pronounced relaxor properties: the maximum of the dielectric constant is diffuse and its temperature, T m, increases by more than 70 K with an increase in the frequency from 102 to 106 Hz. It is assumed that the unusual properties of the PbFe1/2Ta1/2O3 crystals are caused by mesoscopically inhomogeneous compositional ordering and comparatively high conductivity providing favorable conditions for the appearance of the volume-charge and thermal electron polarization. 相似文献