高压下Co在Zr46.755Ti8.25Cu7.5Ni10Be27.5大块金属玻璃过冷液相区中的扩散

通过离子注入结合二次离子质谱分析方法,研究了高压下Co在Zr46.75Ti8.25Cu7.5Ni1oBe27.5大块金属玻璃过冷液相区中的扩散行为.在603 K时,Co在Zr46.75Ti8.25Cu7.5Ni10Be27.5大块金属玻璃中的扩散系数随压力的增大而增大,其扩散激活体积ΔV*=-1.236Ω,Ω是合金的平均原子体积.结果表明,在热平衡状态下Co在Zr46.75Ti8.25Cu7.5Ni10Be27.5大块金属玻璃中的扩散是通过间隙机理进行的.     

大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5的流变行为研究

采用静态拉伸方法在连续升温条件下动态地测量了大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5（Vit1）的黏度随温度的变化关系.在应变速率与温度的关系曲线中，观测到了与玻璃转变和晶化过程相联系的多个应变速率峰.在玻璃转变温度Tg以上，大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5的过冷液体呈现Newton流体特征，其黏度与温度的关系符合Vogel Fulcher-Tammann (VFT)关系式，拟合得到脆度D*＝36，VFT温度T0＝319K，脆度参数m＝30，这说明Zr41T 关键词： 大块金属玻璃 应变速率 剪切黏度 自由体积     

大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5的流变行为研究

采用静态拉伸方法在连续升温条件下动态地测量了大块金属玻璃Zr41 Ti14Cu12.5Ni10Be225(Vitl)的黏度随温度的变化关系.在应变速率与温度的关系曲线中,观测到了与玻璃转变和晶化过程相联系的多个应变速率峰.在玻璃转变温度Tg以上,大块金属玻璃Zr41Ti14Cu125Ni10Be225的过冷液体呈现Newton流体特征,其黏度与温度的关系符合Vogel-Fulcher-Tammann(VFT)关系式,拟合得到脆度D*=36,VFT温度T0=319K,脆度参数m=30,这说明Zr41 Ti14Cu12.5Ni10Be225的过冷液体是一种类似于硅酸盐类的"强"液体.在玻璃转变温度Tg以下,粘度与温度的关系偏离VFT关系,从结构弛豫的观点出发,借助金属玻璃的自由体积模型对其进行了分析和讨论.     

压力对Zr46.75Ti8.25 Cu7.5Ni10Be27.5大块非晶合金玻璃转变和晶化动力学的影响

利用X射线衍射和差示扫描量热分析研究了高温高压下Zr46.75Ti8.25Cu7.5Ni10Be27.5大块非晶合金的玻璃转变和晶化行为,结果发现压力降低了该大块非晶合金中的自由体积、热焓和晶化激活能.     

块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5的超导与负电阻温度系数

测量了块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5在退火前后其电阻值随温度的变化,测量的温度范围为1.5-300K.样品在退火前后都发现有超导现象.零磁场下其超导转变温度Tc分别为1.84和3.76K.在5-300K温度范围内,原始样品具有负的电阻温度系数.如果取Zr,Ti,Cu,Ni及Be分别贡献出1.5,1.5,0.5,0.5及两个传导电子,则可以用扩展的Faber-Ziman理论去解释原始样品的负电阻温度系数.还对块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5在温度范围5-300K之间的R(T)曲线用一个多项式进行了拟合.     

金属玻璃的断裂机理与其断裂韧度的关系

本文选取了三种不同断裂韧度值的金属玻璃Zr41.25Ti13.75Ni10Cu12.5Be22.5,Ce68Al10Cu20Co2和Fe41Co7Cr15Mo14Y2C15B6,通过压缩实验测量了它们的应力-应变关系;样品断裂以后观察了其断口形貌,发现这三种金属玻璃具有不同的断裂模式.经过对这三种金属玻璃做缺口三点弯曲实验,利用数字散斑技术研究了缺口前端应变集中方向弹性应变场的演化过程.根据金属玻璃的屈服准则,阐述了不同断裂韧度值的金属玻璃的断裂机理.     

大块金属玻璃Al7.5Cu17.8Ni10.7Zr64的耐Ar12+离子辐照性能研究北大核心CSCD

利用能量为3 MeV的Ar12+离子辐照金属玻璃Al7.5Cu17.8Ni10.7Zr64和金属W,研究了金属玻璃的Ar离子辐照损伤,辐照剂量分别为1×1014,1×1015和1×1016 ions/cm2。XRD分析发现在不同剂量辐照下Al7.5Cu17.8Ni10.7Zr64均保持非晶为主要结构。不同剂量辐照后的金属玻璃样品表面没有明显的辐照损伤,而金属W在剂量为1×016 ions/cm2时表面出现大面积不规则的裂纹和孔洞。AFM分析显示Al7.5Cu17.8Ni10.7Zr64的表面均方根粗糙度随辐照剂量的增大而增大;辐照后金属玻璃的表面硬度略有降低,而金属W的硬度有所升高。在低于金属玻璃的玻璃化转变温度时,金属玻璃Al7.5Cu17.8Ni10.7Zr64的耐Ar12+溅射能力好于金属W。     

聚变堆第一镜材料块体金属玻璃表面特性

研究了块体金属玻璃（块体非晶合金）Zr65Al7.5Ni10Cu17.5, Co61.2B26.2Si7.8Ta4.8和金属多晶钼3种第一镜材料经低温等离子体H和Ar辐照后的表面特性变化。结果表明,两种块体金属玻璃的抗H等离子体溅射能力与其成分有关。随着等离子体辐照时间的增加,金属多晶钼和块体金属玻璃Zr65Al7.5Ni10Cu17.5的表面粗糙度增大,镜面反射率降低;而块体金属玻璃Co61.2B26.2Si7.8Ta4.8的表面粗糙度减小,镜面反射率升高。X射线衍射仪（XRD）分析表明,块体金属玻璃在离子体溅射过程中,表面微结构具有自修复性。     

注入Mo 在Zr57Nb5Cu15.4Ni12.6Al10非晶合金中的扩散

通过二次离子质谱仪(SIMS)研究了Mo在Zr57Nb5Cu15.4Ni12.6Al10非晶合金中的扩散,并计算出其扩散激活能Q和前置系数D0分别为1.95 eV和1.13×10-5 m2s-1.根据Stokes-Einstern关系式研究了玻璃转变温度以下593-673 K之间Zr57Nb5Cu15.4Ni12.6Al10非晶合金的黏滞特性,得到的黏滞系数从593 K的1.07×1010Poise降到673 K的1.42×108 Poise.     

块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5的超导与负电阻温度系数

测量了块体金属玻璃Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5在退火前后其电阻值随温度的变化,测量的温度范围为1.5—300K.样品在退火前后都发现有超导现象.零磁场下其超导转变温度T_c分别为1.84和3.76K.在5—300K温度范围内,原始样品具有负的电阻温度系数.如果取Zr, Ti, Cu, Ni及Be分别贡献出1.5, 1.5, 0.5, 0.5及两个传导 关键词： 块体金属玻璃 超导 电阻温度系数     

Topological Superconductivity in Cu(x)Bi(2)Se(3)

A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator Cu(x)Bi(2)Se(3), which superconducts below ～3 K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting Cu(x)Bi(2)Se(3) present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in Cu(x)Bi(2)Se(3). In addition, we found an unusual pseudogap that develops below ～20 K and coexists with the topological superconducting state.     

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)

Y-type hexaferrites with tunable conical magnetic structures are promising single-phase multiferroics that exhibit large magnetoelectric effects. We have investigated the influence of Co substitution on the magnetoelectric properties in the Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)(x = 0.0, 0.4, 1.0, 1.6). The spin-induced electric polarization can be reversed by applying a low magnetic field for all the samples. The magnetoelectric phase diagrams of BaBa(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22) are obtained based on the measurements of magnetic field dependence of dielectric constant at selected temperatures. It is found that the substitution of Co ions can preserve the ferroelectric phase up to a higher temperature, and thus is beneficial for achieving single-phase multiferroics at room temperature.     

N(2)-Broadening Coefficients in the nu(1) Band of (35)Cl(12)C(14)N

N(2)-broadening coefficients have been measured for 30 lines of cyanogen chloride ((35)Cl(12)C(14)N) at room temperature in the P and R branches of the nu(1) band, using a tunable diode-laser spectrometer. These lines, with J values ranging from 0 to 55, are located in the spectral range 694-736 cm(-1). The collisional widths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. The broadenings coefficients of (35)ClCN-N(2) have also been calculated from a semiclassical theory involving the atom-atom Lennard-Jones model for the intermolecular potential in addition to electrostatic interaction. Copyright 2000 Academic Press.     

Torsional Splitting in the nu(5) Fundamental Infrared Band of CH(3)CD(3) and (13)CH(3)CD(3)

The nu(5) fundamental (C-C stretching) of CH(3)CD(3) shows a resolved torsional structure, caused by perturbations due mainly to the linear dependence of the torsional potential barrier on the normal coordinate Q(5). We were able to analyze this structure and to assign vibration-rotation transition wavenumbers for all five torsional components, classified according to the symmetry species of the G(18)((3)) extended molecular group. The torsional splitting pattern is qualitatively similar to that of a nondegenerate vibrational state with an even number of excited torsional quanta v(6). Explorative calculations show that the main perturber system should consist of the torsional components of the vibrational ground state correlating with v(6)=4 in the high barrier limit. The strength of the perturbation on the E(r0) torsional components of nu(5) increases rapidly with r, the E(40) component being the most affected. The observed transition wavenumbers can be reasonably fitted by a simplified model containing independent effective vibration-rotation parameters for the five different torsional components of nu(5), for both CH(3)CD(3) and (13)CH(3)CD(3). The trend of the determined values of the effective vibrational wavenumbers and rotational parameters over the torsional components supports the proposed vibration-torsion interaction mechanism, responsible for the observed torsional splittings. A strong anomaly observed in the rotational intensity distribution of nu(5) is discussed. Copyright 2001 Academic Press.     

The (29)Si T(1) and T(2) NMR relaxation in porous paramagnetic material SiO(2)-MnO-Al(2)O(3)

The (29)Si spin-lattice relaxation in porous silica-based material 1, doped by ions Mn(2+) at a Si/Mn ratio of 3.5, is non-exponential, independent of magic-angle spinning (MAS) rates and governed by direct dipolar coupling between electron and nucleus where an electron relaxation time is estimated to be about 10(-8)s. In the absence of mutual energy-conserving spin flips (spin diffusion) in 1, the (29)Si T(2) time increases linearly with spinning rates. None was observed in diamagnetic porous system 2. The unexpected (29)Si T(2) dependence has been interpreted in terms of the large bulk magnetic susceptibility (BMS) effects. It has been shown that editing the (29)Si Hahn-echo MAS NMR spectra eliminates wide lines, belonging to (29)Si nuclei in the proximity of paramagnetic centers, and reduces the BMS broadenings in sideband patterns for nuclei remote from these centers.     

Multiple magnetic transitions in single crystals of Ce_(12)Fe_(57.5)As_(41) and La_(12)Fe_(57.5)As_(41)

Measurements of magnetic and transport properties were performed on needle-shaped single crystals of Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41).The availability of a complete set of data enabled a side-by-side comparison between these two rare earth compounds.Both compounds exhibited multiple magnetic orders within 2-300 K and metamagnetic transitions at various fields.Ferromagnetic transitions with Curie temperatures of 100 and 125 K were found for Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41),respectively,followed by antiferromagnetic type spin reorientations near Curie temperatures.The magnetic properties underwent complex evolution in the magnetic field for both compounds.An antiferromagnetic phase transition at about 60 K and 0.2 T was observed merely for Ce_(12)Fe_(57.5)As_(41).The field-induced magnetic phase transition occurred from antiferromagnetic to ferromagnetic structure.A strong magnetocrystalline anisotropy was evident from magnetization measurements of Ce_(12)Fe_(57.5)As_(41).A temperature-field phase diagram was present for these two rare earth systems.In addition,a logarithmic temperature dependence of electrical resistivity was observed in the two compounds within a large temperature range of 150-300 K,which is rarely found in 3D-based compounds.It may be related to Kondo scattering described by independent localized Fe 3d moments interacting with conduction electrons.     

Inhomogeneous low frequency spin dynamics in La(1.65)Eu(0.2)Sr(0.15)CuO(4)

We report Cu and La nuclear magnetic resonance measurements in the title compound that reveal an inhomogeneous glassy behavior of the spin dynamics. A low temperature peak in the La spin lattice relaxation rate and the "wipeout" of Cu intensity both arise from these slow electronic spin fluctuations that reveal a distribution of activation energies. Inhomogeneous slowing of spin fluctuations appears to be a general feature of doped lanthanum cuprate.     

Self-diffusion of (31)Si and (71)Ge in relaxed Si(0.20)Ge(0.80) layers

Self-diffusion of implanted (31)Si and (71)Ge in relaxed Si(0.20)Ge(0.80) layers has been studied in the temperature range 730-950 degrees C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6 eV and 3.5 eV and preexponential factors of 7.5 x 10(-3) m(2) s(-1) and 8.1 x 10(-3) m(2) s(-1) for (31)Si and (71)Ge , respectively. These results suggest that, as in Ge, in Si(0.20)Ge(0.80) both (31)Si and (71)Ge diffuse via a vacancy mechanism. Since in Si(0.20)Ge(0.80) (71)Ge diffuses only slightly faster than (31)Si , in self-diffusion studies on Si-Ge (71)Ge radioisotopes may be used as substitutes for the "uncomfortably" short-lived (31)Si radiotracer atoms.     

Superconductivity in Restricted Chromo-Dynamics (RCD) in SU(2) and SU(3) Gauge Theories

Characterizing the dyonically condensed vacuum by the presence of two massive modes (one determining how fast the perturbative vacuum around a colour source reaches the condensation and the other giving the penetration length of colored flux) in SU(2) theory, it has been shown that due to the dynamical breaking of magnetic symmetry the vacuum of RCD acquires the properties similar to those of relativistic superconductor. Analysing the behaviour of dyons around RCD string, the solutions of classical field equations have been obtained and it has been shown that magnetic constituent of dyonic current is zero at centre of the string and also at the points far away from the string. Extending RCD in the realistic color gauge group SU(3), it has been shown that the resulting Lagrangian leads to dyonic condensation, color confinement and the superconductivity with the presence of two scalar modes and two vector modes.     

Recording of second-harmonic index gratings in photorefractive (K(0.5) Na(0.5))(0.2) (Sr(0.75) Ba(0.25))(0.9) Nb(2)O(6) crystals

We propose and demonstrate a novel method for recording second-harmonic volume index gratings in photorefractive crystals. The fundamental component of the index grating is eliminated by means of a pi -phase shifted double-exposure process that uses the Mach-Zehnder interferometric technique. Experimental results for (K(0.5) Na(0.5)) (0.2)(Sr> (0.75)Ba (0.25))(0.9)Nb (2)O(6) crystals are presented and discussed.