Heavy alkali metal-arsenic alloy-based graphite intercalation compounds: Investigation of their synthesis and of their physical properties

Heavy alkali metal-arsenic alloys intercalate easily into graphite, leading to the formation of a new family of ternary graphite intercalation compounds (GICs). Pure phases formulated as MAsxC4s (M = K, Rb or Cs; s = stage; x ≤ 1) have been synthesized at the laboratory. This article aims to expose all physical measurements performed on these intercalation compounds to get an idea about their electronic properties.Electrical conductivity measurements have been performed both parallel and perpendicular to the basal planes, between 4.2 and 295 K. Room temperature resistivity values lie between 16 and 35 μΩ cm and the anisotropic resistivity takes a value of an order of magnitude of 10⁴. Dynamic magnetic susceptibility measurements, carried out at low temperature on some phases, showed that they do not exhibit superconducting transition up to 1.3 K. Raman spectroscopy investigation, which is a useful tool to study the electronic and the chemical stability of GICs, highlighted a significant up-shift of the G-band of the carbon intra-layer vibration frequency, compared to the pure graphite vibration mode. Undoubtedly, this is related to the electronic charge transfer established between graphite layers and intercalated species.     

An explanation for deviations from the quark number scaling of elliptic flows in low pT region

We carry out a systematic study of the different contributions to the deviations of the elliptic flows from the quark number scaling in high energy heavy ion collision in a quark combination model.The effects that we considered are:the resonance decay,the flavor dependence of the quark elliptic flow and the combination of quarks/antiquarks with slightly different transverse momenta.Our results show that the deviations observed in experiments can be well reproduced within the combination framework if all the three effects are considered. We make a detailed analysis of the different contributions using a Monte-Carlo program and suggest measuring the quark number scaling in intermediate pT range more precisely.     

Magnetic and Transport Properties of Tm2Co7B3 Compound

Magnetic and transport properties of Tm₂Co₇B₃ compound have been studied. This compound crystallizes in the hexagonal Ce₂Co₇B₃ type structure. The coercivity (H _c) of the compound was determined from hysteresis measurements in fields up to 4 T. The temperature dependence of coercivity has been explained by a thermally activated process of domain wall motion. The resistivity at low temperatures shows a T ² dependence. At higher temperatures the resistivity is not a linear function of temperature, which indicates an electron-phonon interaction in the presence of a small s-d scattering.     

Structural and Physical Properties of New Conducting Cation Radical Salts with Te-Based Counteranions, Tetraiodotellurate(II) and Hexaiododitellurate(II)

This article reports preparation, structure, and conducting property of several cation radical salts of organic donors tetramethyltetrathiafulvalene (TMTTF), ethylenedithiotetrathiafulvalene (EDT-TTF), bis(ethylenedithio)tetrathiafulvalene (ET), bis(ethylenedithio)tetraselenafulvalene (BETS) and hexamethylenetetraselenafulvalene (HMTSF) with two novel planar Te-based dianions, TeI₄²⁻ and Te₂I₆²⁻. (ET)₅Te₂I₆ 1 and (BETS)₅Te₂I₆ 2 are isostructural. In these Te₂I₆²⁻ salts, intermolecular short I···I contacts form a supramolecular corrugated anion sheet. Donor arrangement is similar to the θ-type. With lowering temperature, the resistivity of 1 shows a gradual increase followed by a sharp upturn at 110 K. 2 is metallic down to 120 K and shows a gradual increase of the resistivity followed by a clear transition to an insulating state around 60 K. Crystal structure of (ET)₄TeI₄ 3 is based on the “herring bone” arrangement of ET molecules similar to the α-type. 3 shows a semiconductive behavior around room temperature followed by a transition to an insulating state at 210 K. (EDT-TTF)₄TeI₄ 4, a semiconductor, exhibits a unique two-dimensional arrangement of dimerized EDT-TTF molecules.     

射频溅射法制备Pb_(1-x)Co_xSe薄膜及物性研究

利用复合靶共溅射法制备了半磁性半导体 Ｐｂ１－ ｘ Ｃｏｘ Ｓｅ 薄膜．研究了薄膜的成分结构以及电阻率温度特性和磁化率温度特性间的关系．结果表明：由于 Ｃｏ 离子介入, Ｐｂ１－ ｘ Ｃｏｘ Ｓｅ 发生了由金属特性向半导体特性的转变,在充分低的温度下,并伴有磁相转变．磁相转变温度与磁性离子浓度相关,磁化率的相对变化幅度与磁性离子浓度有关     

Tailoring magnetism in artificially structured materials: the new frontier

The current standard of electronic devices and data storage media has reached a level such that magnetic materials have to be fabricated on a nanometer scale. In particular, the emerging concept of spintronics, which is based on fact that current carriers have not only charge but also spin, requires the assembling of nanometer-sized magnetic structures with desired magnetic properties. It is this background that motivates scientists and engineers to attempt to grow and characterize magnetic objects at smaller and smaller length scales, from 2D films and multilayers to 1D wires and eventually to 0D dots. In this article, some of the most significant progress in recent years in the effort of growing artificially structured magnetic materials are reviewed. The new structural and magnetic properties of these materials are discussed, with an emphasis on the correlation between structure and magnetism, which also serves as guidance for improving their magnetic properties. The emerging emphasis is on converting the existing knowledge into growing and studying low-dimensional complex materials, which promise to have considerably higher “tuning” ability for desired properties.     

Electronic structure of non-magnetic impurities in dilute alloys of Al

The electronic structure of substitutional non-magnetic impurities Cu, Ag, Cd, Mg, Zn, Ga, In, Ge, Si and Sn in Al is studied using density functional theory. A simple physical model is proposed to calculate the effective charges on impurities in trivalent metal Al. A linear relation is found between the effective charges on impurities and impurity vacancy capture radii. The spherical solid model (SSM) is used to account for discrete nature of the host. The impurity-induced change in charge density, scattering phase shifts, host-impurity potential, residual resistivity and impurity self-energy are calculated. Higher order scattering phase shifts are found significant and the host-impurity potential is found proportional to effective charge on impurity in its vicinity. The self-consistently calculated potential is used to calculate the electric field gradients (EFGs) at the first and second nearest neighbours (1NNs, 2NNs) of impurity. The calculated values are in agreement with the experimental results.     

新型塑料导线直径在线测量系统

本文提出了一种用线阵ＣＣＤ非接触实时测量塑料导线直径的仪器，它有如下特点：（１）采用了对被测目标所发出的烟雾不敏感的光学系统，提高了测量精度；（２）采用工作于脉冲方式的大功率近红外ＬＥＤ做照明光源，其寿命比采用白炽灯作为光源大为增长，同时缩小了体积并有利于抑制可见光的干扰；（３）对电信号采用了两级滤波、直流恢复、自适应阈值二值化等处理技术；（４）采用定标的方法来消除目标位置移动的影响，提高了测量精度，降低了加工装配精度要求。现场使用证明，它能长期可靠地工作，总的测量误差小于±０．０２ｍｍ。     

Atomic short-range order in CuMn alloys

The establishment of atomic short-range order (SRO) has been investigated in CuMn alloys (5, 8,13,16,20 at. % Mn) by measurement of the electrical resistivity during isochronal and isothermal annealing. An increasing degree of SRO is accompanied by a reduction of resistivity; this effect increases with Mn concentration. For 8,13 and 16 at. % Mn SRO kinetics turn out to deviate significantly from single exponential behavior with a maximum at 13 at. % Mn, whereas at 5 and 20 at. % Mn SRO is adjusted in a single exponential process. For data analysis three methods are used: a sum of two and three exponentials as well as a log-normal spectrum of relaxation times. The strong interaction between second-nearest-neighbor atoms in CuMn seems to be essential for SRO kinetics but of minor importance for the value of SRO-induced resistivity change.     

Superconductivity in Sr<Subscript>0.75</Subscript>Y<Subscript>0.75</Subscript>Ba<Subscript>1.5</Subscript>Cu<Subscript>3</Subscript> O<Subscript>7−<Emphasis Type="Italic">d</Emphasis></Subscript> compounds

The effect of simultaneous Sr substitution at the Ba and Y sites has been studied in the Sr_0.75Y_0.75Ba_1.5Cu₃O_7–dsystem. Attempts to replace 25% Y and 25% Ba have been successful and superconductivity was observed above 78 K for Sr_0.75Y_0.75Ba_1.5Cu₃O_7–d compound with high oxygen content, i.e., O_6.76, and having orthorhombic crystal symmetry. The compound was treated in argon gas at 800°C to reduce the oxygen content and to induce some structural changes. The Sr_0.75Y_0.75Ba_1.5Cu₃O_6.1 compound thus obtained has tetragonal symmetry and low oxygen content, O_6.1. It has also shown superconductivity at 28 K. The paper presents a careful comparison of the structural and electrical properties and infrared absorbance spectra of the two compounds with the same metallic composition, Sr_0.75Y_0.75Ba_1.5Cu₃, but with different oxygen content and crystal symmetry. The study clearly establishes the occurrence of superconductivity in tetragonal Sr-substituted (both at Y and Ba sites in) YBCO.