合金元素对Ag/Al界面性质影响的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算和分析Ag(111)/Al(111)界面体系的能量与电子结构,讨论Ag中加入的Be、Mg、Al、Ca、Ni、Sn合金化元素对Ag/Al界面性质的影响.结果表明:Ni原子倾向于界面处的取代位置,而Be、Mg原子倾向于靠近界面处的取代位置,Al、Ca、Sn原子倾向于远离界面处的取代位置;合金元素Be、Mg、Al、Ca、Ni、Sn的加入均会使Ag/Al界面的稳定性降低,其中Ca元素的影响程度最大,分离功降低到0.923 J/m~2,界面能增至0.703 J/m~2;通过电子结构计算结果分析认为,导致界面稳定性下降的主要原因应是合金化元素的加入使界面间形成的Ag-Al共价键强度降低引起.     

新型TPBI/Ag阴极结构的红色有机发光二极管

采用可溶液加工的小分子红光材料2为发光层（EML）,制备了不同阴极结构的系列电致发光器件.结果表明,空穴阻挡层（HBL）TPBI的引入能有效降低高功函数（Al, Ag, Au）金属阴极的电子注入势垒,显著改善器件发光效率,与传统阴极结构（Ba/Al）比较,采用TPBI/Ag阴极结构的器件外量子效率提高了57%,主要原因是TPBI/Ag阴极界面形成较低的电子注入势垒,有利于电子注入,使器件发光效率明显提高. 关键词： 电致发光 电子注入 阻挡层 高功函数金属阴极     

Si-Li合金嵌锂性能和弹性性能的第一性原理计算

采用基于密度泛函理论的第一性原理平面波赝势方法,计算了锂离子电池硅负极材料在嵌Li过程中形成Li_xSi合金相(0≤x≤4.4)的形成能、嵌Li电位、晶体结构、电子结构和弹性性能.计算结果表明,随着嵌Li量的增加,Li_xSi合金体系总量能逐渐降低,Li_xSi合金相的形成能均为负值,表明硅负极材料的嵌Li反应在热力学可以自发进行;随着嵌Li量的增加,Li_xSi合金相的平均嵌Li电位逐渐降低,体积膨胀率逐渐增大,这与实验测得的结果具有良好的一致性.Li_xSi合金相在费米能级附近的电子主要由Si原子的p电子和Li原子的s电子共同贡献,Li_xSi合金相的费米能态密度随着嵌Li量的增加在整体上呈现增大趋势,电子导电性增强.随着嵌Li量的增加,Li_xSi合金相的体积模量(B)、剪切模量(G)和杨氏模量(E)逐渐降低,G/B值表明Li_xSi合金相均呈脆性,导致硅在嵌Li过程容易发生脆性结构破坏.     

Fe-Cr-Al合金氧化膜形成机理电子理论研究

通过自编软件建立了Fe-Cr-Al合金表面、氧化膜/基体界面模型,采用递归法计算了合金元素在Fe-Cr-Al合金表面、氧化膜/基体界面的环境敏感镶嵌能、亲和能、结合能、态密度等电子结构参数.从电子层次系统研究了Fe-Cr-Al合金氧化膜的形成机理、稀土元素和杂质硫对氧化膜形成过程及黏附性的影响机理.研究表明Fe-Cr-Al合金中Al的偏聚驱动力远大于Y,Cr.氧化初期氧从合金表面向合金内部扩散,合金内部Al向合金表面扩散,使合金形成富铝、氧表面层;氧与Al间的亲和力较大（亲和能低）,氧原子容易与Al结合生成Al₂O₃保护膜;合金中加入Y后,Y在合金表面偏聚,抑制Al向合金表面扩散,氧化膜的横向生长得到有效控制,从而避免氧化膜皱褶形貌的发生,提高氧化膜的黏附性;合金内部的S通过扩散汇集在基体/氧化膜界面,S使界面区原子的总能增高,总态密度降低,减小了界面的稳定性,进而削弱氧化膜与合金基体的结合力. 关键词： 电子结构 高温氧化 Fe-Cr-Al合金     

Si-Li合金相嵌锂性能和弹性性能的第一性原理计算

采用基于密度泛函理论的第一性原理平面波赝势方法,计算了锂离子电池硅负极材料在嵌Li过程中形成LixSi合金相(0≤x≤4.4)的形成能、嵌Li电位、晶体结构、电子结构和弹性性能。计算结果表明,随着嵌Li量的增加,LixSi合金体系总量能逐渐降低,LixSi合金相的形成能均为负值,表明硅负极材料的嵌Li反应在热力学可以自发进行;随着嵌Li量的增加,LixSi合金相的平均嵌Li电位逐渐降低,体积膨胀率逐渐增大,这与实验测得的结果具有良好的一致性。LixSi合金相在费米能级附近的电子主要由Si原子的p电子和Li原子的s电子共同贡献,LixSi合金相的费米能态密度随着嵌Li量的增加在整体上呈现增大趋势,电子导电性增强。随着嵌Li量的增加,LixSi合金相的体积模量(B)、剪切模量(G)和杨氏模量(E)逐渐降低,G/B值表明LixSi合金相均呈脆性,导致硅在嵌Li过程容易发生脆性结构破坏。     

Si-Li合金相嵌锂性能和弹性性能的第一性原理计算

采用基于密度泛函理论的第一性原理平面波赝势方法,计算了锂离子电池硅负极材料在嵌Li过程中形成LixSi合金相(0≤x≤4.4)的形成能、嵌Li电位、晶体结构、电子结构和弹性性能。计算结果表明,随着嵌Li量的增加,LixSi合金体系总量能逐渐降低,LixSi合金相的形成能均为负值,表明硅负极材料的嵌Li反应在热力学可以自发进行;随着嵌Li量的增加,LixSi合金相的平均嵌Li电位逐渐降低,体积膨胀率逐渐增大,这与实验测得的结果具有良好的一致性。LixSi合金相在费米能级附近的电子主要由Si原子的p电子和Li原子的s电子共同贡献,LixSi合金相的费米能态密度随着嵌Li量的增加在整体上呈现增大趋势,电子导电性增强。随着嵌Li量的增加,LixSi合金相的体积模量(B)、剪切模量(G)和杨氏模量(E)逐渐降低,G/B值表明LixSi合金相均呈脆性,导致硅在嵌Li过程容易发生脆性结构破坏。     

第一性原理研究合金元素对逆变奥氏体在Cu沉淀上异质形核的影响

超高强度马氏体钢的力学性能强烈依赖于逆变奥氏体的形状、尺寸及含量.通常,提高逆变奥氏体含量,有助于改善超高强度钢的塑韧性.对含Cu马氏体淬火钢时效处理时, Cu粒子会在马氏体组织边界沉淀,并作为质点促进逆变奥氏体形核.为了探索不同合金元素对逆变奥氏体在Cu沉淀上异质形核的影响,本文利用第一性原理方法研究了合金元素X (X=Cr, Al, Mo, W, Ni, Co, Mn)对Cu/γ-Fe界面性质的影响,并分析了合金原子替换界面处Cu和Fe原子前后界面的黏附功、界面能和电子结构.研究结果表明,合金元素Cr,Mo, W, Mn替换Cu/γ-Fe界面处Cu原子时, Cu/γ-Fe界面处产生强烈的X—Fe共价键,黏附功增大且界面能减小,显著提高界面稳定性,促进γ-Fe在Cu沉淀上异质形核.而替换界面处Fe原子时,界面稳定性变化很小,掺杂原子与相邻的其他原子成键较弱.     

Ta和Re对Ni/Ni3Al相界面断裂强度和蠕变强度的影响

采用基于密度泛函理论和广义梯度近似的第一原理方法,探究Ta元素和Re元素在Ni/Ni3Al相界面中的相互作用及其对界面强度的影响.计算表明:在绝大多数化学计量比范围内, Ta原子优先占据γ相中的顶点Ni位, Re原子优先占据γ’相中的Al位, Re原子和Ta原子共合金化时掺杂位置不发生改变.通过格里菲斯断裂功、不稳定堆垛层错能及空位迁移能的计算,得出Ta和Re合金化都可以增强界面的格里菲斯断裂能,提高界面的结合强度,两种合金化元素均提高了体系的不稳定堆垛层错能,即提高了界面阻碍位错运动的能力和抵抗变形的能力,其中Re的单独合金化效果更好.两种元素的掺杂提高了界面上空位迁移的势垒,阻碍了空位的发射和吸收,进而提高了合金的蠕变能力.     

铝锂合金样品的前处理及其Ag和Li的光谱分析

针对铝锂合金样品检测其Ag和Li,采用等离子体原子发射光谱法(ICP-OES)同时测定Ag和Li,火焰原子吸收光谱法(FAAS)分别测定Ag和Li,单宁酸分光光度法(VS)测Ag,对不同的光谱测定方法进行了比较,证明了ICP-OES检测铝锂合金中的Ag和Li具有较高的抗干扰性。对比了三种不同的样品消解方法,确定了FAAS测Li采用王水溶样最佳,ICP-OES,FAAS和VS测Ag采用HCl+H₂O₂体系溶样准确度更高。详细讨论了样品中共存元素Al, Mg, Zr, Ti, Cu的干扰及消除方法。用氨水沉淀消除共存元素Al,Ti,Zr,8-羟基喹啉沉淀分离Mg和Cu的方法消除原子吸收光度法测Ag的干扰;采用磷酸盐沉淀分离Ti而消除原子吸收光度法测Li的干扰;采用与原子吸收光度法测银相同的消除干扰方法,消除上述离子干扰,滤去干扰沉淀后,用硝酸赶盐酸解蔽Ag+离子,同时分解消除8-羟基喹啉的颜色,以消除分光光度法测银的干扰。对比消除干扰前后的结果发现准确度显著提高,证明消除干扰的方法切实有效。将选择的最佳消解体系和干扰消除方法应用于铝锂合金样品的测定,ICP-OES测Li和Ag回收率分别在100.39%～103.01%和100.42%～103.73%之间,FAAS测Li和Ag 回收率分别在95.91% ～99.98%和98.04%～103.67%之间,分光光度法测Ag回收率在98.00%～101.00%之间,测定结果满足分析要求。     

Al、Zn、Mn、Zr、Ca对Mg合金电子结构影响的第一性原理研究

应用密度泛函理论研究了合金元素Al、Zn、Mn、Zr、Ca对α-Mg合金电子结构的影响。对合金元素添加后的结构进行了优化。在稳定结构的基础上,通过对不同合金元素的形成能、态密度、布居分布、差分电荷密度的分析,认为引起合金性能变化的原因是各合金元素的电负性和原子半径的大小不同所致,对比了合金元素对材料电子结构的影响,从理论上解释了Zr、Ca强烈的合金强化、细化作用。     

Effect of solute atoms on grain boundary sliding in magnesium alloys

The effect of solid-solution alloying on grain boundary sliding (GBS) was investigated using pure magnesium and six kinds of Mg–X (X?=?Ag, Al, Li, Pb, Y and Zn) dilute binary solid solutions with an average grain size of 10?µm. A sharp increase in damping capacity caused by GBS was observed above a certain temperature. The temperature at which a sharp increase in damping capacity occurred depended on the alloying element. The addition of Y and Ag markedly increased the onset temperature (more than 100?K) for a sharp increase in damping capacity, whereas the addition of Zn, Al and Li slightly increased the onset temperature (less than 50?K) as compared with that for pure magnesium. Tensile tests at a temperature of 423?K revealed that the higher the onset temperature, the lower the strain rate sensitivity of the flow stress. It is suggested that the former elements (Y and Ag) are more effective in suppressing GBS in magnesium alloys than the latter ones (Zn, Al and Li). The suppression of GBS was associated with low grain boundary energy, and the extent to which the energy is reduced depended on the alloying element. It was suggested that the change in the lattice parameter (the so-called c/a ratio) affects the grain boundary energy, and thus, the occurrence of GBS.     

Solute-second phase interaction for Mg,Ag and Zn in Al–Li alloys

ABSTRACT

Early experiments have shown the promises of alloying with Mg?+?Ag (or Mg?+?Zn) on the performance of Al–Li alloys. To better understand the interaction between solutes and second phases in Al–Li alloys, Mg, Ag and Zn segregation to Al/δ′ interface as well as their substitution in δ′ bulk were investigated at the atomic level using first principles modelling and calculations. Energetics results and local charge analyses revealed that Mg, Ag and Zn can segregate to Al/δ′ interface by different preference, but have no significant influence on the interface adhesion. Ag and Zn can also dissolve into δ′ bulk, and enhance the local metallic bonding with nearest-neighboring Al atoms. Based on these results, a multi-fold benefit mechanism was suggested for the combined alloying with Mg?+?Ag (or Mg?+?Zn) in Al–Li alloys.     

Impurity doping into Mg2Sn: A first-principles study

We studied the formation energy and atomic structure of impurities in Mg₂Sn using first-principles plane-wave total energy calculations. Twenty elements, namely H, Li, Na, K, Rb, Sc, Y, La, Cu, Ag, Au, B, Al, Ga, In, N, P, As, Sb, and Bi, were selected as the impurity species. We considered structural relaxation of the atoms within the second nearest neighbors of the impurity atom in the 48-atom supercell. The results of the formation energy calculations suggested that Sc, Y, La, P, As, Sb, and Bi are good n-type dopants whereas Li and Na are good p-type dopants. The electrical properties of Li-, Na-, and Ga-doped Mg₂Sn and La-doped Mg₂(Si, Sn) composites reported previously can be explained by the low formation energies of Li, Na, Ga, and La in Mg₂Sn.     

Energetics and electronic structure of refractory elements in the dislocation of NiAl

Using DMol and the discrete variational method within the framework of the density functional theory,we study the alloying effects of Nb,Ti,and V in the [100](010) edge dislocation core of NiAl.We find that when Nb(Ti,V) is substituted for Al in the center-Al,the binding energy of the system reduces 3.00 eV(2.98 eV,2.66 eV).When Nb(Ti,V) is substituted for Ni in the center-Ni,the binding energy of the system reduces only 0.47 eV(0.16 eV,0.09 eV).This shows that Nb(Ti,V) exhibits a strong Al site preference,which agrees with the experimental and other theoretical results.The analyses of the charge distribution,the interatomic energy and the partial density of states show that some charge accumulations appear between the impurity atom and Ni atoms,and the strong bonding states are formed between impurity atom and neighbouring host atoms due mainly to the hybridization of 4d5s(3d4s) orbitals of impurity atoms and 3d4s4p orbitals of host Ni atoms.The impurity induces a strong pinning effect on the [100](010) edge dislocation motion in NiAl,which is related to the mechanical properties of the NiAl alloy.     

DFT study of BaTiO<Subscript>3</Subscript> (001) surface with O and O<Subscript>2</Subscript> adsorption

Progress of scanning tunneling microscopy (STM) allowed to handle various molecules adsorbed on a given surface. New concepts emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale is thus particularly invaluable. In this work, within the framework of density functional theory (DFT), we present an electronic and structural ab initio study of a BaTiO₃ (001) surface (perovskite structure) in its paraelectric phase. As far as we know the atomic and molecular adsorption of oxygen at surface is then analyzed for the first time in the literature. Relaxation is taken into account for several layers. Its analysis for a depth of at least four layers enables us to conclude that a reasonable approximation for a BaTiO₃ (001) surface is provided with a slab made up of nine plans. The relative stability of two possible terminations is considered. By using a kinetic energy cut off of 400 eV, we found that a surface with BaO termination is more stable than with TiO₂ termination. Consequently, a surface with BaO termination was chosen to adsorb either O atom or O₂ molecule and the corresponding calculations were performed with a coverage 1 on a (1×1) cell. A series of cases with O₂ molecule adsorbed in various geometrical configurations are also analyzed. For O₂, the most favorable adsorption is obtained when the molecule is placed horizontally, with its axis, directed along the Ba-Ba axis and with its centre of gravity located above a Ba atom. The corresponding value of the adsorption energy is -9.70 eV per molecule (-4.85 eV per O atom). The molecule is then rather extended since the O–O distance measures 1.829 ?. By comparison, the adsorption energy of an O atom directly located above a Ba atom is only -3.50 eV. Therefore we are allowed to conclude that the O–O interaction stabilizes atomic adsorption. Also the local densities of states (LDOS) corresponding to various situations are discussed in the present paper. Up to now, we are not aware of experimental data to be compared to our calculated results.     

Al原子在Pb基底上的沉积过程研究

利用分子动力学方法模拟了Al原子在Pb基底上的沉积过程. 对Al原子在Pb基底(001)面上沉积的形态与Pb原子在Al(001)基底上沉积的形态做了比较. 由于界面间势垒的不同, 两个体系界面间的形态有明显的差异. 分析了基底温度、基底晶面指向、沉积原子的入射动能对界面间原子混合的影响. 模拟结果显示: 随着基底温度升高, 基底原子的可移动性大大增加, 与沉积原子发生较大程度的混合; 入射能的改变对界面间原子的混合影响很小; 基底表面取不同的晶格指向时, 基底与沉积原子间的混合行为也有明显的不同. 利用径向分布函数分析了沉积原子的入射能对薄膜中原子排列有序性的影响. 较高入射能对应更有序的薄膜结构; 由径向分布函数的结构可以推测Al原子在Pb(001)基底表面沉积时界面间可能有金属间化合物生成. 关键词： Pb/Al体系 沉积过程 分子动力学 入射能     

第一性原理计算Ni原子吸附在Al(111)表面原子结构和电子态

利用密度泛函理论和广义梯度近似研究镍吸附在Al(111)表面。在覆盖率为0.25ML下,分析了Ni吸附在Al(111)表面的面心立方洞位、六角密排洞位、顶位和桥位四个高对称位的原子结构和吸附能。比较不同高对称位的吸附能发现,六角密排洞位的吸附能最大,是5.76 eV,是最稳定的吸附位置。详细讨论了两个最低能量结构-三重洞位的电子结构、功函数、表面偶极距和Ni-Al键的特性。在费米能级附近,Ni-3d和Al-3s,3p轨道产生杂化,形成金属间化合键。由于吸附导致双金属体系表面偶极距和功函数的变化。我们发现：Ni原子与Al(111)表面原子间成建主要是共价键,没有表现出明显的静电荷跃迁,相应的产生非常小的表面偶极距。与面心立方洞位相比,六角密排洞位在费米能级附近产生较低的态密度,在键态附近产生较大的杂化。     

Alloying behaviors of AgMg,AuMg and AgAl alloys

An expression of the structure-dependent energy of simple metal-noble metal binary alloy is given on the basis of the pseudopotential method. The energy is expressed as a sum of three parts; a band-structure energy, an electrostatic energy and a repulsive overlap energy, each of which is characterized by the usual long-range and short-range order parameters.The energy in a disordered state and the ordering energy are calculated for the AgMg, AuMg and AgAl systems, using the pseudopotential form factors and the overlap potentials of noble metals given by Moriarty. The numerical results reproduce qualitatively the observed phase diagrams; the existences of β- and ?-phases in the AgMg system, of β-phase in AuMg and of β- and ζ-phases in AgAl. The L2₀-type ordered phase (β′-phase) of AgMg alloy which remains ordered up to the melting point is well explained. Further, an estimation of the local ordering energy suggests that a clustering appears in the Al-rich region of AgAl alloy. However, the calculations fail to interpret the ordering behavior of β′-phase in the AuMg system and the short-range order of Ag-rich AgAl alloy. The role of individual terms of the structure-dependent energy on alloying is discussed.     

The growth mode of aluminium on silver (111)

The geometric and electronic structures occuring during the growth of Al on a single crystal Ag(111) surface have been studied using a combination of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), energy loss spectroscopy (ELS) and work function measurements. The Auger signal versus deposition time plots, which were used to monitor the growth mode, are shown to behave in an identical fashion to that expected for layer-by-layer (Frank-van der Merwe) growth. LEED was used to determine the lateral periodicity of thin Al films and shows that Al forms, at very small coverages, 2D islands which have the same structure as the Ag(111) substrate and which grow together to form the first monolayer. At substrate temperatures of 150 K a well defined (1 × 1) structure with the same orientation as the underlying Ag(111) can be seen up to at least 12 ML. After completion of the third monolayer the ELS spectrum approached that observed for bulk aluminium. At a coverage of 3 ML the work function decreases by 0.4 eV from the clean silver value.