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1.
For the first time, 64Cu tracer measurements of ionic diffusion were performed for several copper-rich glass compositions in the CuI---As 2Se 3, CuI---SbI 3---As 2Se 3, CuI---PbI 2---As 2Se 3, CuI---PbI 2---SbI 3---As 2Se 3 and Cu 2Se---As 2Se 3 systems. In accordance with previous a.c. impedance results and Wagner d.c. polarization measurements, it was found that pure Cu + ion-conducting glasses (50CuI---17PbI 2---33As 2Se 3 and 50CuI---20PbI 2---10SbI 3---20As 2Se 3) exhibit the highest copper tracer diffusion coefficients, DCu, and the lowest diffusion activation energies. The values of DCu at room temperature are higher by 4.5–5.5 orders of magnitude than those in an As 2Se 3 glass. The Haven ratio, HR, is found to be 0.52–0.61 (ternary glass) and 0.93–1.00 (quaternary glass). Short-range diffusional displacements of the iodide ions induced by the hopping Cu + ions are also detected in the CuI---PbI 2---SbI 3---As 2Se 3 glassy system using 129I-Mössbauer spectroscopy in the temperature range of 4.2 to 305 K. The activation energy of local hopping, Eh ≈ 0.31 eV, is very similar to that of bulk ionic conductivity (0.37 eV) and copper diffusion (≈ 0.33 eV). In contrast to CuI-based vitreous alloys, 50Cu 2Se---50As 2Se 3 glass exhibits DCu that are two to five orders of magnitude lower, and the copper ion transport number, tCu+, is between 10 −3 and 10 −4 in the temperature range 140–170 °C. 相似文献
2.
根据密度泛函理论的第一性原理计算了具有非中心反演对称的异质结δ-(Zn,Cr)S(111)体系的原子结构和电子结构.Cr原子之间通过第一层S原子传递磁性相互作用.结合广义布洛赫条件,又进一步计算了反方向的自旋螺旋能量与波矢的色散关系E(q)与E(-q).E(q)与E(-q)能量之差反映了δ-(Zn,Cr)S(111)的S层与Cr层之间空间反演对称性破缺引起的DMI的大小.通过海森伯相互作用(HBI)模型与Dzyaloshinsky-Moriya作用(DMI)模型拟合第一性原理计算值,得到了Cr原子间各近邻的HBI参数J_1-J_4与DMI参数d-_1,d_2.在δ-(Zn,Cr)S(111)中,Cr原子间的耦合为M型反铁磁.DMI参数d_1为-0.53 meV,为顺时针手性DMI,在δ-(Zn,Cr)S(111)界面上有可能会产生斯格明子.本文计算表明,磁性和非磁性半导体界面有可能存在DMI,为理论研究和磁存储技术的进步开拓一个新的方向. 相似文献
3.
The two-orbital Hubbard model is studied numerically by using the Hartree-Fock approximation in both real space and momentum space, and the ground-state properties of the alkali metal iron selenide semiconducting KFe 1.5Se 2 are investigated. A rhombus-type Fe vacancy order with stripetype antiferromagnetic (AFM) order is found, as was observed in neutron scattering experiments [J. Zhao, et al., Phys. Rev. Lett. 109, 267003 (2012)]. Hopping parameters are obtained by fitting the experimentally observed stripe AFM phase in real space. These hopping parameters are then used to study the ground-state properties of the semiconductor in momentum space. It is found to be a strongly correlated system with a large on-site Coulomb repulsion U, similar to the AFM Mott insulator — the parent compound of copper oxide superconductors. We also find that the electronic occupation numbers and magnetizations in the dxz and dyz orbitals become different simultaneously when U> Uc (~3.4 eV), indicating orbital ordering. These results imply that the rotational symmetry between the two orbitals is broken by orbital ordering and thus drives the strong anisotropy of the magnetic coupling that has been observed by experiments and that the stripe-type AFM order in this compound may be caused by orbital ordering together with the observed large anisotropy. 相似文献
4.
Mössbauer studies on 57Fe-doped superconducting REBa 2Cu 3O 7+δ (RE=Er, Dy) were made as a function of temperature for x=0.15 and 0.30. The magnetic behavior of the 3d dopants, which mainly occupy Cu(1) sites, undergoes antiferromagnetic ordering which is coexistent with superconductivity at low temperature. The dimensionality of the magnetic interaction changes from 2D to 3D when the rare earth changes from Er to Dy. the line-widths of the Mössbauer subspectra are characteristic of magnetic fluctuation behavior in the vicinity of a phase transition. Combining these results with those of Fe-doped Y-123 (pseudo 1D) and Gd (3D), the magnitude of the rare earth moments appears to be strongly correlated with the dimensionality of the magnetic interaction of Fe dopants in these compounds. However, the Mössbauer spectrum for 155Gd in GdBa 2Cu 2.85Fe 0.15O 7+δ ( TN(Fe) 14 K) shows no magnetic order at 4.9 K. 相似文献
5.
Lattice spacings, as magnetic susceptibilities, ESR, specific heats, and electrical properties have been measured on the cointercalation compounds of 1T-CdI 2 type host TiS 2, Fe xCo
TiS 2 (0 x
) and (Fe yCo 1−y)
TiS 2(0 y 1). While the interlayer spacings are expanded rather smoothly with increasing the cointercalated Fe metals, the magnetic, thermal, and transport properties depend sensitively on a small amount of the added Fe metals, showing the presence of strong magnetic interactions, or guest-guest interactions between the cointercalated Fe and Co 3d metals in these systems. 相似文献
6.
Using high-resolution angle-resolved and time-resolved photoemission spectroscopy, we have studied the low-energy band structures in occupied and unoccupied states of three ternary compounds GeBi 2Te 4, SnBi 2Te 4 and Sn 0.571Bi 2.286Se 4 near the Fermi level. In previously confirmed topological insulator GeBi 2Te 4 compounds, we confirmed the existence of the Dirac surface state and found that the bulk energy gap is much larger than that in the first-principles calculations. In SnBi 2Te 4 compounds, the Dirac surface state was observed, consistent with the first-principles calculations, indicating that it is a topological insulator. The experimental detected bulk gap is a little bit larger than that in calculations. In Sn 0.571Bi 2.286Se 4 compounds, our measurements suggest that this nonstoichiometric compound is a topological insulator although the stoichiometric SnBi 2Se 4 compound was proposed to be topological trivial. 相似文献
7.
We have studied the electronic and magnetic structures of the ternary iron arsenides AFe 2As 2 (A = Ba, Ca, or Sr) using the first-principles density functional theory. The ground states of these compounds are in a collinear antiferromagnetic order, resulting from the interplay between the nearest and the next-nearest neighbor superexchange antiferromagnetic interactions bridged by As 4p orbitals. The correction from the spin–orbit interaction to the electronic band structure is given. The pressure can reduce dramatically the magnetic moment and diminish the collinear antiferromagnetic order. Based on the calculations, we propose that the low energy dynamics of these materials can be described effectively by a t−J H−J 1−J 2-type model [arXiv: 0806.3526v2, 2008]. 相似文献
8.
The magnetic structures and some relevant bulk magnetic properties of R(Cu, Ni) 2 (R = Tb, Tb zY 1−z, Dy, Ho, Er and Tm) are summarized. Basically, the magnetic structures are antiferromagnetically modulated with propagation vector
a *. For R = Tb, Dy, Ho the a-axis anisotropy dominates and the structures are longitudinally modulated. For R = Tm, Er (probably) the b-axis anisotropy dominates and this results in transversely modulated structures. For R = Tb, Dy the structures are collinear, For R = Ho, Er, Tm (probably) an incommensurate modulation coexists with the commensurate a *-axis modulation at the lowest temperature. 相似文献
9.
Three-dimensional Heisenberg model in the form of a tetrahedron lattice is investigated. The concurrence and multipartite entanglement are calculated through 2-concurrence C and 4-concurrence C4. The concurrence C and multipartite entanglement G4 depend on different coupling strengths Ji and are decreased when the temperature T is increased. For a symmetric tetrahedron lattice, the concurrence C is symmetric about J1 when J~ is negative while the multipartite entanglement G4 is symmetric about J1 when J2 〈 2. For a regular tetrahedron lattice, the concurrence G of ground state is 1/3 for ferromagnetic case while G = 0 for antiferromagnetic ca.se. However, there is no multipartitc entanglement since C4=0 in a regular tetrahedron lattice. The external magnetic field 13 can increase the maximum value of the concurrence GB and induce two or three peaks in Cn. There is a peak in the multipartite entanglement G4 B when G4B is varied as a function of the temperature T. This peak is mainly induced by the magnetic field B. 相似文献
10.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
11.
This study is focused on calculation of the electronic structure and optical properties of non-metal doped Sb2Se3 using the first-principles method. One and two N atoms are introduced to Sb and Se sites in a Sb 2Se 3 crystal. When one and two N atoms are introduced into the Sb 2Se 3 lattice at Sb sites, the electronic structure shows that the doping significantly modifies the bandgap of Sb 2Se 3 from 1.11 eV to 0.787 and 0.685 eV, respectively. When N atoms are introduced to Se sites, the material shows a metallic behavior. The static dielectric constants ε1(0) for Sb 16Se 24, Sb 15N 1Se 24, Sb 14N 2Se 24, Sb 16Se 23N 1, and Sb 16Se 22N 2 are 14.84, 15.54, 15.02, 18.9, and 39.29, respectively. The calculated values of the refractive index n(0) for Sb 16Se 24, Sb 15N 1Se 24, Sb 14N 2Se 24, Sb 16Se 23N 1, and Sb 16Se 22N 2 are 3.83, 3.92, 3.86, 4.33, and 6.21, respectively. The optical absorbance and optical conductivity curves of the crystal for N-doping at Sb sites show a significant redshift towards the short-wave infrared spectral region as compared to N-doping at Se sites. The modulation of the static refractive index and static dielectric constant is mainly dependent on the doping level. The optical properties and bandgap narrowing effect suggest that the N-doped Sb 2Se 3is a promising new semiconductor and can be a replacement for GaSb due to its very similar bandgap and low cost. 相似文献
12.
X-ray photoelectron spectroscopy (XPS) of the Se 3 d peak for Se in Se, SeO 2, As 2Se 3, ZnSe, CdSe, CoSe, FeSe, CrSe, VSe 2 and TiSe were studied. It was found that, firstly, in the case of As 2Se 3, ZnSe, CdSe, CoSe and CrSe, as the change in electronegativity of the anion increases, the change in the binding energy value of the Se 3 d peak also increases and, secondly, in all of the Se compounds studied, the Se-Se bond in pure Se is stronger than the Se-x bond, where X = As, Zn, Cd, Co, Fe, Cr, V and Ti. 相似文献
13.
采用双时格林函数方法研究了自旋为1的双层平方晶格阻挫模型的相变行为.详细探讨了层间耦合相互作用J c和单离子各向异性参数D对奈尔态(AF1)和共线态(AF2)之间相转换的影响.结果显示:只要参数J c和D不同时为零,奈尔态和共线态在J 2=J 1/2(这里J 1和J 2分别描述的是系统自旋间最近邻和次近邻交换作用)时的相变温度相等,两个态共存.在低于相变点的温度范围内,AF1-AF2态之间可以发生相转换,其相变类型为一阶相变.当J 2≠J 1/2时,尽管AF1-AF2态有不同相变温度,但它们也可以共存.如果AF1(AF2)态的相变温度大,在低温,AF1(AF2)态更稳定;在高温,AF2(AF1)态更稳定;在中间温度范围内,AF1-AF2态之间也可以发生一阶相转换. 相似文献
14.
The excitonic properties of a ZnSe/ZnS xSe 1−x strained quantum well (QW) are calculated taking into account interface effects. Numerical results obtained with ZnS 0.18Se 0.82/ZnSe QWs show that graded interfaces can be responsible for a strong broadening of excitonic spectra. 相似文献
15.
基于密度泛函微扰理论,运用第一性原理研究两种终结面的Bi 4Se 3薄膜的声子结构和电-声子相互作用.结果表明两种终结面的Bi 4Se 3薄膜体系都是动力学稳定的. Bi 4Se 3薄膜中插入的Bi 2双原子层与Bi 2Se 3五原子层的声子投影态密度并不完全匹配,这会阻碍部分声子的输运,降低热导,从而有利于提高材料的热电性能.另外,两种终结面的Bi 4Se 3薄膜的电-声子耦合系数都不太大(约0.278),有利于制备基于室温工作的电子学器件. 相似文献
16.
硒化锑(Sb 2Se 3)是一种二元单相化合物, 原料储量大、毒性低、价格便宜; 同时其禁带宽度合适(~1.15 eV), 吸光系数大(>10 5 cm -1), 长晶温度低, 非常适合制作新型低成本低毒的薄膜太阳能电池, 理论光电转换效率可达30%以上. 目前文献报道的Sb 2Se 3薄膜太阳能电池效率已达3.7%, 初步证明了Sb 2Se 3材料在薄膜太阳能电池应用方面的巨大潜力. 本文综述了近年来Sb 2Se 3太阳能电池的研究进展, 着重介绍了Sb 2Se 3的材料特性和薄膜制备及相关理论研究, 阐述了不同结构电池器件的研究进展, 并对其发展趋势进行了展望. 相似文献
17.
R 2(Fe, Co) 14B compounds (R = Y, Nd and Gd) were prepared in high purity. The magnetic behavior of R 2(Fe, Co) 14B compounds is reported over the temperature range 4 to 300 K. The effects of Fe substitution by Co on the saturation magnetization, Curie temperature and anisotropy are presented. The spin-reorientation temperature is lowered as Co replaces Fe. This also results in a reduced cone angle. The R2Fe14−xCoxB alloys crystallize in the tetragonal structure over the entire concentration range of 0 x 14. When Fe is substituted by Co, the Curie temperature increases significantly, the saturation magnetization increases to a maximum value around x = 2, and the anisotropy becomes planar for R = Y and Gd. The Nd2(Fe, Co)14B systems all exhibit uniaxial anisotropy at room temperature and Nd2Co14B is strongly uniaxial at 77 K. The Nd2(Fe, Co)14B systems are conical at 77 K. 相似文献
18.
The synthesis of combinatorial Bi 2−xSb xSe 3 thin films by arrested precipitation technique (APT) using triethanolamine-bismuth, triethanolamine-antimony and sodium selenosulphite as sources of Bi 3+, Sb 3+ and Se 2−, respectively is investigated on commercial glass substrates. The growth mechanism of film formation, composition and surface morphology of the as deposited films were studied as a function of preparative parameters and bath composition. The films were monophasic, polycrystalline and covered the surface of the substrate completely. Energy dispersive X-ray analysis gave coherent elemental composition indicating single phase BiSbSe 3 was made. The good results obtained for Bi 2−xSb xSe 3 thin films revealed that arrested precipitation technique is best suited for the deposition of large area thin films on conducting/nonconducting substrates to produce materials for device applications. 相似文献
19.
The RCo 2 and R 2Fe 17 compounds (R = rare earth) exhibit Invar-like thermal expansion anomalies below their ordering temperatures. These spontaneous volume magnetostrictions are discussed by considering their magnetic properties. In RCo 2 compounds there is no intrisinc Co-moment is induced by the exchange and applied fields. The volume expansion anomaly is associated with the onset of the 3d magnetic moment. IN R 2Fe 17 compounds there is an intrisinc Fe- moment. Magnetic structures give evidence for positive and negative exchange interactions between Fe atoms which are strongly distance dependent. The thermal expansion anomaly is a result of this distance of the magnetic interactions. 相似文献
20.
A series of substituted lead iron niobate compounds with the general formula Pb 2+(1−x)A Zx(Fe {(1−(2−Z)x)/2}Nb {(1+(2−Z)x)/2})O 3 (0< x<0.6 and A=La 3+, K + or Sr 2+) were prepared by a modified solid-state synthesis. The relative concentrations of Fe 3+ and Nb 5+ were adjusted to compensate the charge imbalance due to the aliovalent substitution. The dielectric constant and magnetic susceptibilities were studied as a function of temperature. The temperature of the dielectric maximum, TM, of the substituted compounds decreased linearly with increasing concentration of the substituent ions. The magnetic measurements showed an antiferromagnetic transition at temperatures TN1 due to the superexchange interactions mediated by Fe–O–Fe and an additional antiferromagnetic-type transition at TN2. TN1 linearly increased with the increasing concentration of Fe 3+ ion at the B-site of ABO 3-type substituted compounds. TM is shown to be directly dependent on the concentration of the ferroactive Nb 5+ ions at the B-site and Pb 2+ ions at the A-site. 相似文献
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