Si1-xGex合金半导体中CiCs和CiOi缺陷随Ge含量的变化

采用从头计算(ab initio)的方法对Si和Si_1-xGe_x合金半导体材料中C_iC_s缺陷的性质进行探讨，同时也对比调查了C_iO_i缺陷在Si和Si_1-xGe_x合金中的性质. 在不同Ge含量的Si_1-xGe_{x相似文献}   

三明治结构Tan(B3N3H6)n+1 团簇的磁性和量子输运性质

利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Ta_n(B₃N₃H₆)_n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Ta_n(B₃N₃H₆)_n+1团簇耦合到Au电极上时, 形成的Au-Ta_n(B₃N₃H₆)_n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器.     

铌酸钾钠基无铅透明陶瓷制备及性能

采用传统固相烧结工艺, 结合特殊的气氛控制技术,制备了铌酸钾钠(KNN)基无铅透明陶瓷 xBa(Sc_0.5Nb_0.5)O₃-(1-x) (K_0.5N_0.5)NbO₃ (简写xBSN-(1-x)KNN). 并对其微观结构、介电、铁电性能和光学透光率进行了研究. 结果表明该体系陶瓷具有准立方钙钛矿结构, 没有其他杂相, 晶粒大小与可见光波长相当, 高度致密, 无明显的晶界存在. 在 x=0.05时, d₃₃最高可达到110 pC/N, 2P_r达到25.4 μC/cm². 同时该材料具有良好的透明性, 在可见光范围内,透过率达到54%左右, 近红外2500 nm处,透过率接近83%, 是一种有望取代铅基透明陶瓷的环境友好型无铅透明陶瓷.     

Multiferroic properties of solben gel derived Bi5Fe1-xCoxTi3O15 thin films

Co-doped Bi₅FeTi₃O₁₅ thin films (BFCT-x, Bi₅Fe_1-xCo_xTi₃O₁₅) were prepared using a sol—gel technique. XRD patterns confirm their single phase Aurivillius structure, and the corresponding powder Rietveld analysis indicates the change of space group around x=0.12. The magnetic hysteresis loops are obtained and ferromagnetism is therefore confirmed in BFCT-x thin films. The remanent magnetization (M_r) first increases and reaches the maximum value of 0.42 emu/cm³ at x=0.12 due to the possible Fe³⁺—O—Co³⁺ ferromagnetic coupling. When x = 0.25, the M_r increases again because of the dominant Fe³⁺—O—Co³⁺ ferromagnetic coupling. The remanent polarization (2P_r) of BFCT-0.25 was measured to be as high as 62 μC/cm², a 75% increase when compared with the non-doped BFCT-0 films. The 2P_r remains almost unchanged after being subjected to 5.2 × 10⁹ read/write cycles. Greatly enhanced ferroelectric properties are considered to be associated with decreased leakage current density.     

源于“团簇-共振”模型的理想金属玻璃电子化学势均衡

理想金属玻璃是指完全满足电子结构稳定性的金属玻璃. 在我们前期工作中提出的“团簇加连接原子"及理想金属玻璃的“团簇-共振"结构模型的 基础上, 本文指出理想金属玻璃应该满足电子化学势均衡判据, 可定量给出团簇与连接原子的比例, 最终确定了理想金属玻璃成分式[团簇](连接原子)_x. 运用此判据, 解析了Cu-Zr基和Co-B基块体金属玻璃, 实验确定的最佳形成能力成分满足电子化学势均衡.     

Hydrogen storage of Mg1-xMxH2 (M=Ti, V, Fe) studied using first-principles calculations

In this work, the hydrogen storage properties of the Mg-based hydrides, i.e., Mg_1-xM_xH₂ (M=Ti, V, Fe, 0 ≤ x ≤ 0.1), are studied using the Korringa-Kohn-Rostoker (KKR) calculation with the coherent potential approximation (CPA) approximation. In particular, the nature and the concentrations of the alloying elements and their effects are studied. Moreover, the material's stability and hydrogen storage thermodynamic properties are discussed. In particular, we find that the stability and the temperature of desorption decrease without significantly affecting the storage capacities.     

第一性原理计算ZrnFe(n=2—13)团簇的基态结构及其磁性

从第一性原理出发，利用密度泛函理论中的广义梯度近似对Zr_nFe(n=2—13)团簇进行了结构优化、能量和频率计算.在充分考虑自旋多重度的前提下，对每一具体尺寸的团簇，得到了多个平衡构型，并根据能量高低确定了团簇的基态结构.综合团簇的结合能、二阶能量差分以及团簇的最高占据轨道和最低未占据轨道间的能隙可知Zr₅Fe，Zr₇Fe和Zr₁₂Fe团簇的稳定性相对较高，Zr₁₂Fe团簇的结构是具有I_h对称性的正二十面体，而且Zr₁₂Fe的稳定性在所有团簇中是最高的.另外，不仅Zr₅Fe，Zr₇Fe和Zr₁₂Fe团簇的稳定性相对较高，而且它们均为磁性团簇(而Zr_n团簇的磁矩在n≥5时已经发生了淬灭)，由此可知通过选择合适的掺杂元素可能得到高稳定的磁性团簇.从Mulliken布居分析结果可知，除了在Zr₁₂Fe团簇中Fe原子失去少量电荷外，其他团簇中Fe原子均从Zr原子那里得到了一定量电荷，即Fe原子在Zr_nFe(n=2—13，n≠12)团簇中是电子受体.     

Tb0.3Dy0.7－xPrx(Fe0.9Al0.1)1.95合金的磁致伸缩、自旋重取向和穆斯堡尔谱研究

系统研究了室温下Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95 (x=0，0.1，0.2，0.25，0.3，0.35)合金中稀土元素Pr替代Dy对晶体结构、磁致伸缩、各向异性和自旋重取向的影响. 结果发现，x≤0.1时，Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95完全保持MgCl₂立方Laves相结构，0.1<x≤0.3，有杂相出现并且随Pr替代量逐渐增多；晶格常数a随Pr含量x的增加缓慢增大. 磁致伸缩测量发现，随着替代量x的增多磁致伸缩减小；x>0.2时超磁致伸缩效应消失. 然而，x=0.1时合金的磁致伸缩略大于没有替代的，而且磁致伸缩随磁场更易趋于饱和，说明Pr替代有助于降低磁晶各向异性. 内禀磁致伸缩λ₁₁₁随Pr替代量x的增加接近线性增加. 由相对磁化率随温度的变化关系可以看出，自旋重取向温度随Pr替代量的增多呈先增后降趋势，在x=0.1处出现极大值. 穆斯堡尔效应表明，随Pr含量的增加Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95合金中易磁化轴可能在{110}面上绕主对称轴作微小转动，发生自旋重取向. 与Al元素替代效应相比，Pr替代Dy对自旋重取向的影响相对较小.     

FeCo二元合金纳米线阵列的磁化反转

利用交流电化学沉积方法在氧化铝模板中制备了一维结构的Fe_xCo_1-x(0 ≤ x ≤ 0.51)二元合金纳米线阵列.X射线衍射结果显示,单质Co纳米线为(100)择优取向的hcp结构,FeCo合金纳米线则呈现(110)择优取向的bcc结构,而且衍射峰随纳米线中Fe含量的增加向低角度偏移.室温磁性测量结果显示, FeCo合金纳米线具有较好的磁特性.与Co纳米线相比,Fe的引入改善了Co纳米线的磁性能,使其呈现出较大的矫顽力和较高的矩形比.采用一致转动模型和对称扇形机理的球链模型分别计算了FeCo合金纳米线的矫顽力, 发现其磁化反转机理与对称扇形机理的球链模型相符合.     

TiGen-(n=7~12)团簇的光电子能谱及密度泛函理论研究

利用光电子能谱及密度泛函理论计算对TiGe_n^-(n=7~12)团簇的几何结构及电子特性等进行了系统研究. 对于TiGe_n^-负离子及中性TiGe_n,在n=8时出现了钛原子半内嵌的船型结构;在n=9~11时,新增的锗原子加盖到这种船型结构上,逐步形成钛原子完全内嵌的结构. TiGe₁₂^- 团簇具有一种钛原子内嵌的变形六棱柱结构. 自然布居分析结果显示,对于n=8~12的TiGe_n^-/0 团簇,随着内嵌结构的形成,有电子从锗原子转移到钛原子,说明其电荷转移方式与结构演变密切相关.     

Role of Ga-doping in ironben gallium alloy clusters

The structural and magnetic properties of Fe_n-mGa_m (n=3～6, m=0～2; n=13, m=0～3) alloy clusters have been studied using density functional theory. The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites. The Ga-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters, along with a decrease of the local magnetic moments of Fe atoms around Ga dopants. These findings provide a microscopic insight into Fe-Ga alloys which are well-known magnetostriction materials.     

二元室温金属流体热导率的理论计算与实验研究

室温金属流体在芯片散热领域中正日益显示重要价值,但相关材料的热物性比较缺乏.本文基于Faber-Ziman理论和Wiedemann-Franz-Lorenz定律,采用Ashcroft-Langrethp硬球模型偏结构因子以及空核心模型赝势计算了液态二元镓铟及钠钾合金的热导率.结果表明:相比于钠钾合金的热导率随原子组分浓度呈抛物线变化,镓铟合金的热导率与原子组分浓度呈单调变化关系,同时镓铟合金的热导率随着温度升高而升高.作为对比,本文同时也对镓铟合金的热导率进行了实验测定.结合所获数据及钠钾合金文献数据对比,表明计算结果与实验值符合得较好.本文工作为进一步研究二元合金热导率打下了基础.     

Calculation of the surface tension of liquid Ga-based alloys

As known, Eyring and his collaborators have applied the structure theory to the properties of binary liquid mixtures. In this work, the Eyring model has been extended to calculate the surface tension of liquid Ga–Bi, Ga–Sn and Ga–In binary alloys. It was found that the addition of Sn, In and Bi into Ga leads to significant decrease in the surface tension of the three Ga-based alloy systems, especially for that of Ga–Bi alloys. The calculated surface tension values of these alloys exhibit negative deviation from the corresponding ideal mixing isotherms. Moreover, a comparison between the calculated results and corresponding literature data indicates a good agreement.     

Thermodynamics and surface properties of liquid Al–Ga and Al–Ge alloys

The surface properties of Al–Ga and Al–Ge liquid alloys have been theoretically investigated at a temperature of 1100 K and 1220 K respectively. For the Al–Ga system, the quasi chemical model for regular alloy and a model for phase segregating alloy systems were applied, while for the Al–Ge system the quasi chemical model for regular and compound forming binary alloys were applied. In the case of Al–Ga, the models for the regular alloys and that for the phase segregating alloys produced the same value of order energy and same values of thermodynamic and surface properties, while for the Al–Ge system, the model for the regular alloy reproduced better the thermodynamic properties of the alloy. The model for the compound forming systems showed a qualitative trend with the measured values of the thermodynamic properties of the Al–Ge alloy and suggests the presence of a weak complex of the form Al₂Ge₃. The surface concentrations for the alloys show that Ga manifests some level of surface segregation in Al–Ga liquid alloy while the surface concentration of Ge in Al–Ge liquid alloy showed a near Roultian behavior below 0.8 atomic fraction of Ge.     

递归法研究Pt对Ti合金腐蚀影响

采用递归法计算了Ti及Ti合金的电子态密度、环境敏感镶嵌能、费米能级和格位能等电子结构参量.计算发现Pt在晶体中环境敏感镶嵌能和格位能高于表面,从电子层面证实Pt易在 Ti合金表面偏聚.偏聚在表面的Pt有序能为正值,故Pt以有序相（Pt与Ti的化合物）形式分布在合金表面.晶体表面Pt 与Ti的化合物电极电位较低,它与Ti形成微电池.在腐蚀介质的作用下,Pt与Ti的化合物分解,Pt沉淀到晶体表面造成Pt在合金表面形成凹凸不平的Pt电催化层.Pt电催化层加强Ti钝化作用,从而提高了Ti合金的抗腐蚀能力. 关键词： 电子结构 Ti合金表面 钝化     

Pd对Ti合金钝化影响的电子理论研究

采用递归法计算了Ti合金的电子态密度、环境敏感镶嵌能、费米能级等电子结构参量.计算发现Pd在晶体体内比在其表面的环境敏感镶嵌能高,说明Pd易于在 Ti合金表面偏聚.Pd在表面时,原子团簇形成能为负值,说明Pd以团簇形式分布于合金表面.态密度计算结果表明,Pd的局域态密度局限在很窄的能量范围内(-20—-15 eV),使Ti合金的总态密度在此区出现尖峰.该尖峰的存在降低了Ti合金的费米能级,于是表面含Pd较多的区域费米能级较低,含Pd少或不含Pd的区域费米能级较高.费米能级不同的两区域接触会形成微电池,在腐 关键词： Ti合金 钝化 电子结构 表面     

Metastable phases in Gallium-Indium eutectic alloy particles and their size dependence

In this paper, submicrometer-sized Ga-In eutectic alloy particles were dispersed into polymethylmethacrylate (PMMA) matrix by ultrasonic vibration and sedimentation method. The solidification and melting processes of Ga-In eutectic alloy particles were studied by differential scanning calorimeter (DSC). Four endothermal peaks with the onset temperature located at 16, −11, −22, and −27 °C were observed in DSC heating curves, which corresponded to the melting process of the stable Ga-In phase α-Ga(In) and three metastable phases of β-Ga(In), δ-Ga(In) and γ-Ga(In), respectively. The stable phase α-Ga(In) can only be formed when the size of alloy particle was larger than 0.58 μm. Conversely, metastable phases β-Ga(In), δ-Ga(In) and γ-Ga(In) are mainly formed. The result shows that phase structures in Ga-In eutectic alloy are size dependent.     

SimCn （m+n≤7）团簇的密度泛函研究

使用密度泛函理论（DFT）的杂化密度泛函B3LYP方法在6-31G*基组水平上对Si_mC_n（m+n≤7）团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构. 并对最稳定结构的平均结合能（E_b）,二阶能量差分（Δ₂E）和能隙（E_g）等进行了理论研究. 结果表明,随着原子个数的增加,SiC二元团 关键词： mC_n （m+n≤7）团簇')" href="#">Si_mC_n （m+n≤7）团簇 密度泛函理论 结构与性质     

Interaction between interstitial hydrogen and substitutional solute atoms in solid solutions of niobium-base ternary alloys

The interaction between interstitial hydrogen and substitutional solute atoms has been investigated by the measurements of the hydrogen solubility and the influence of hydrogen charging on the half-width of the X-ray reflection lines in pure Nb, Nb-5%V, Nb-5%Mo and Nb-5%Ta alloys. In Nb-5%V and Nb-5%Mo alloys, the solubility considerably increases with respect to pure Nb. On the other hand, the solubility hardly changes in Nb-5%Ta alloy. With addition of hydrogen, the half-widths in pure Nb and Nb-5%Ta alloy show a monotonic increase, but in Nb-5%V and Nb-5%Mo alloys they show a minimum. The results are explained by the interaction of hydrogen with substitutional solute atoms. The interaction is considered to be caused by the internal strain induced by the difference in atomic radii between substitutional and solvent (Nb) atoms.     

Role of the chemical ordering on the magnetic properties of Fe–Ni cluster alloys

The spin and orbital moments of fcc Fe-Ni cluster alloys are determined within the framework of a d-band Hamiltonian including the spin-orbit coupling non perturbatively. Different sizes (up to 321 atoms), compositions, and chemical configurations (random alloys as well as core-shell arrays of iron and nickel atoms) are considered in order to reveal the crucial role played by local order and stoichiometry on the magnetic moments of the clusters. Interestingly, we have found considerably reduced average magnetizations for Fe-Ni clusters with Fe cores compared to that of the bulk alloy with the same composition. Indeed, in these configurations not only antiparallel arrangements between the local moments of some Fe atoms within the iron core are found, but also the total magnetization of the surface Ni atoms is significantly quenched. On the opposite, the disordered and Ni-core cluster alloys are characterized by high magnetizations resulting from saturated-like contributions from both Ni and Fe atoms, in agreement with recent ab-initio calculations. In general, the local orbital magnetic moments are strongly enhanced with respect to their bulk values. Finally, the variation of the orbital-to-spin moment ratio with the chemical order is discussed.