碱土金属原子与Ne原子间相互作用势的理论计算

本文基于无任何可调参数的势模型计算了碱土金属原子(Be、Mg、Ca、Sr、Ba)与Ne原子间相互作用势,得到的势能曲线及势阱位置和深度与现有的从头计算结果符合较好.本文的计算结果进一步验证了碱土金属原子与稀有气体原子间交换能主要来自碱土金属原子最外层s电子与稀有气体原子最外层p电子之间的交换作用.     

Ca5N4高压新相的第一性原理研究

通过在氮中引入杂质离子,利用高压手段获得具有新奇结构的多氮化合物是目前被广泛应用的研究方法.钙氮材料在催化、光电方面有着广泛的应用.具有较低电离能的钙(Ca)元素很容易和氮原子形成离子键钙氮化物.高压为寻找新型钙氮化合物提供了全新的技术途径.因此,利用高压方法,通过改变配比的方式,寻找具有新奇特性的钙氮高压结构,是一项非常有意义的工作.本文利用基于密度泛函理论的结构搜索方法,在100 GPa条件下,通过预测得到了一个稳定的Ca5N4相.该结构内部氮原子之间以N-N共价单键键合,氮原子和钙原子之间是离子键相互作用,且钙氮之间的电荷转移量为1.26 e/N atom.能带结构计算表明P 21/c-Ca5N4是一个直接带隙为1.447 eV的半导体结构.最后,系统地给出了该结构的拉曼振动光谱,并指认了拉曼振动模式,为实验合成该结构提供了理论指导.     

红外光谱对碱土金属二元羧酸盐结构的研究

研究了三十种二元羧酸金属盐的红外光谱，讨论了金属离子和二元酸的种类对二元酸盐配位结构的影响。发现Mg盐、Ba盐，Sr盐为螯合配位，Ca盐，Zn盐中同时存在螯合配位和桥式配位，二元酸的种类对羧酸盐配位结构没有影响。对羧酸盐在常温和熔融后的栩位方式和结构上的差异的研究结果表明，Mg盐，Ca盐与Sr盐，Ba盐在熔融后的结构变化不同。     

Optical properties of the surface transition-metal structures in fluoride ionic crystals and peculiarities of their formation during thermal diffusion

The possibility of forming surface films with an elevated concentration of an impurity metal during high-temperature diffusion has been analyzed for a wide series of ionic crystals: LiF with Co, Ni, Mg, Ca, Ba, and Sr impurities; NaF with Co, Mn, Mg, Ca, and Sr; MgF₂ with Co and Ni; and CaF₂ with Co. It is established that films are formed only on alkali halide crystals with impurities of transition metals and are not formed on alkaline earth fluorides with transition metals, as well as on alkali halide crystals activated with other divalent cationic impurities. The dynamics of the increase and decrease in the intensity of centers related to impurity-vacancy dipoles during thermal diffusion is shown. The mechanisms of film formation are explained in terms of the features of growth and structure of ionic crystals with cationic impurities and on the basis of isomorphism rules.     

STARK STRUCTURE OF THE RYDBERG STATES OF ALKALINE-EARTH ATOMS

The Stark effects of the Rydberg states in the alkaline-earth atoms are studied theoretically. Using a method similar to the treatment of alkali atoms, the properties of the Stark states of Mg, Ca, Sr and Ba atoms in the regions far away from the perturbers are investigated. The Stark maps for Mg (n=16, M=0), Ca (n=10, M=0), Sr (n=12, M=0) and Ba (n=13, |M|=0,1) are presented. Topics such as the general methods of calculation, the treatment of fine structure, and the structure of level anti-crossings are discussed. The comparison between the theoretical and experimental Stark maps is satisfactory.     

结构自还原效应对铋掺碱土金属硅磷铝硼玻璃超宽带近红外发光的影响

本文报道了结构自还原对铋掺杂碱土金属硅磷铝硼玻璃超宽带近红外发光性质的影响. 以Eu作为对比, 在空气气氛中采用高温熔融法分别制备了Eu₂O₃和Bi₂O₃掺杂的35SiO₂-25AlPO₄-12.5Al₂O₃-12.5B₂O₃-15RO(R=Ca,Sr,Ba) 玻璃. 结果证实该玻璃中可发生Eu³⁺→Eu²⁺的高温自还原现象, 且随着碱土金属离子半径增大Eu²⁺ 的自还原性减弱; 同样条件下Bi位于1300 nm波段的近红外发光却随之增强, 而位于1100 nm波段近红外发光和源于Bi²⁺的红光则减弱. 根据结构自还原机理及碱土离子半径变化对玻璃近红外超宽带发光性质的影响, 讨论了Bi离子的近红外发光中心的归属. 上述研究表明玻璃结构自还原特性可以为Bi近红外发光机理研究以及高效Bi掺杂超宽带近红外发光玻璃的设计提供一种有效的思路和方法. 关键词： 玻璃 铋掺杂 近红外发光 自还原效应     

Ba8Ga16Si30与Sr8Ga16Ge30电子特性和热性质的研究

采用基于密度泛函理论和平面波赝势技术的CASTEP程序计算了笼状化合物Ba8Ga16Si30与Sr8Ga16Ge30的电子结构,并以此为基础进一步研究了它们的热性质。态密度和布居分析显示,Ba8Ga16Si30中笼上原子间成键趋于共价性,Sr8Ga16Ge30中笼上原子间成键趋于离子性,可以认为Ba8Ga16Si30的稳定性比Sr8Ga16Ge30强。带结构显示Ba8Ga16Si30与Sr8Ga16Ge30均为金属。热性质研究中提出一个新的模型,模型中认为Ba8Ga16Si30的笼内Ba原子和笼上Ga原子做爱因斯坦振荡,笼上Si原子做德拜运动,这种模型能够更好地描述Ba8Ga16Si30的热导。     

Surface states due to deposited alkaline earth cations on ZnO

Surface states due to Be, Mg, Ca, Sr, and Ba ions deposited on ZnO as salts with varying anions have been examined, to make available a selection of nonvolatile surface states for later study, and to provide a relatively simple group of substitutional surface states that could be used to compare theories with experiment. The results indicate that Be⁺⁺ and Ba⁺⁺ additions lead to shallow acceptor levels, near or above the ZnO conduction band, while deeper acceptor levels (as low as 0.9 eV below the conduction band) are associated with Mg⁺⁺, Ca⁺⁺, and Sr⁺⁺ additions. The energy of the resulting surface state depends somewhat on whether the alkaline earth species is added as the hydroxide or the fluoride. There is evidence of a high density donor level at 1.1 eV below the conduction band perhaps associated with surface lattice oxygen or with OH^? groups. Arguments arepresented suggesting that the surface state is associated with the alkaline earth ions at lattice sites at the ZnO/additive interface, and some of the factors are discussed that must be considered in a theoretical model.     

Unified study of alkaline earth metal

A comprehensive unified study of fcc alkaline earth metal Ca, Sr and the bcc phase of Sr and Ba has been made. Properties studied include equilibrium lattice parameter, total crystal energy, second order elastic constants, pressure derivative of the second order elastic constants and phonon spectrum in the symmetry direction. The results obtained show an overall agreement with experiment. The results partially reproduced the experimentally observed phonon-crossover in Ba, and this has been found as the many-body effect in lattice dynamics.     

硅烯饱和吸附碱金属原子的第一性原理研究

基于密度泛函理论的第一性原理计算, 研究了硅烯饱和吸附碱金属元素原子的稳定性、微观几何结构和电子性质, 并与纯硅烯及其饱和氢化结构进行了对比分析. 研究发现复合物SiX(X=Li, Na, K, Rb)的形成能都是负的, 相对于纯硅烯来说可以稳定存在. Bader电荷分析表明, 电荷从碱金属原子转移至硅原子. 从成键方式来看, 硅烯与氢原子形成共价键, 而与碱金属原子之间形成的键主要是离子性成键, 但还存在部分共价关联成分. 能带计算表明, 锂原子饱和吸附在硅烯形成的复合物SiLi是直接带隙的半导体, 带隙大小为0.34 eV. 其他碱金属饱和吸附在硅烯上形成的复合物都表现为金属性.     

Lamellar phase of stacked two-dimensional rafts of actin filaments

We examined liquid crystalline phases of the cytoskeletal polyelectrolyte filamentous (F-)actin in the presence of multivalent counterions. As a function of increasing ion concentration, the F-actin rods in either an isotropic or a nematic phase will transform into a new and unexpected lamellar phase of cross-linked rafts (L(XR) phase), before condensing into a bundled phase of parallel, close-packed rods. This behavior is generic for alkali earth divalent ions Mg2+, Ca2+, Sr2+, and Ba2+, and the structural transitions are achieved without any architecture-specific actin-binding linker proteins.     

纳米材料中的巨磁电阻效应

纳米材料是指三维空间尺度中至少有一维处于纳米量级的材料,通常为１—１００ｎｍ,如纳米微粒,纳米线、管,纳米薄膜或其组合材料,近年来纳米材料中的巨磁电阻效应颇受人们青睐,本文将重点介绍颗粒膜,颗粒合金薄带,非连续多层膜,颗粒—薄膜混合型膜以及磁性隧道结的巨磁电阻效应。     

Eu3+．Dy3+,Sm3+掺杂Ca(Sr,Ba)W04的光谱性质

采用共沉淀方法制备了稀土离子Eu3+,Dy3+,Sm3掺杂的Ca(Sr,Ba) WO4发光材料,目的是研究金属阳离子改变对稀土离子发光性质的影响.X射线衍射光谱数据表明,CaWO4、SrWO4、BaWO4都是四方晶系I41/a(88)结构,随着阳离子半径增大,衍射峰向小角移动.不同温度制备的BaWO4样品X射线衍射光谱...     

掺杂BaHfO3电子结构与力学性能的第一性原理研究

在广义梯度近似（GGA）下,采用基于密度泛函理论的第一性原理方法研究了掺杂对BaHfO3的电子结构与力学性能的影响．电子结构计算表明：优化的BaHfO3晶格常数与实验值吻合较好,BaHfO3为一种间接带隙的绝缘体材料．掺杂Sr和Ti后该材料仍为间接带隙材料,Ba0.5Sr0.5HfO3的带隙增大,绝缘体特征增强,而BaHf0.5Ti0.5O3的带隙显著减小,呈现出半导体材料的特征．由态密度分析可知,掺杂后带隙的变化主要是由于导带底的移动造成的．力学性能分析表明：与BaHfO3相比,Ba0.5Sr0.5HfO3的剪切模量和杨氏模量均明显减小,材料硬度减弱;BaHf0.5Ti0.5O3的剪切模量及杨氏模量均明显增大,材料硬度增强．电子密度分布分析揭示了掺杂改变体系价电子浓度的分布情况,使BaHfO3的价健特性发生了变化,这是材料硬度改变的内在原因．可见,掺杂能够有效地调控体系的硬度,该研究结果为掺杂BaHfO3力电材料的设计与应用提供了理论依据．     

Electronic Structure and Visible-Light Absorption of Transition Metals(TM=Cr,Mn, Fe,Co) and Zn-Codoped SrTiO_3: a First-Principles Study

First-principles calculations are performed on the influence of transition metal(TM=Cr, Mn, Fe, Co) as codopants on the electronic structure and visible-light absorption of Zn-doped Sr TiO_3. The calculated results show that(Zn,Mn)-codoped Sr TiO_3 requires the smallest formation energy in four codoping systems. The structures of the codoped systems display obvious lattice distortion, inducing a phase transition from cubic to rhombohedral after codoping. Some impurity Cr, Mn and Co 3d states appear below the bottom of conduction band and some Fe 3d states are located above the top of valence band, which leads to a significant narrowing of band gap after transition metal codoping. The enhancement of visible-light absorption are observed in transition metals(TM=Cr, Mn, Fe, Co) and Zn codoped Sr TiO_3 systems. The prediction calculations suggested that the(Zn,Mn)-and(Zn,Co)-codoped SrTiO_3 could be the desirable visible-light photocatalysts.     

Pressure shift and broadening of the resonance lines of singly ionized alkaline-earth atoms and some alkali atoms in hot compressed Ar and He

With a ballistic compressor, the pressure shift and broadening of the resonance lines of singly ionized Ca, Sr and Ba were measured under various pressures of Ar and He at 2400 and 2500°K respectively. To make a comparison with the corresponding effects for alkali atoms, the first member of the principal series and that of the diffuse series of neutral Li and Na-D lines were also studied under the same experimental conditions. By tabulating the results of this paper and previous articles on neutral alkaline-earth resonance lines, it is found that the shift and broadening of the resonance lines of atoms belonging to the three different groups are quite alike. The amounts of shift and broadening taper off slightly in the order of neutral Group (IA), neutral Group (IIA) and singly-ionized Group (IIA) atoms in the periodic table.     

The shift and broadening of the resonance lines of Ca,Sr and Ba in hot,dense argon and helium

The shift and half-width of the resonance singlet lines of Ca, Sr and Ba in emission were measured under various relative densities between 20 and 70 for Ar (at 2500 K) and between 35 and 121 for He (at 2450 K) by means of a ballistic compressor. The shift due to Ar is always red and increased with increasing relative density. The shift due to He is slightly toward red at densities below 50 and then gradually turns to the violet as the relative density is further increased. The foreign gas shift and broadening is nearly the same for the resonance lines of all these different alkaline-earth atoms but is different for different foreign gases, as in the case of alkali metals. Comparison with previous observations of Ca at 910 K shows that the increase of temperature will cause a decrease in red shifts and half-widths.     

A Density Functional Theory Study of Codoping Characteristics of Sulfur with Alkaline Earth in Delafossite CuAlO_2

The structural,electronic properties and formation energies of sulfur and alkaline earth codoped delafossite CuAlO_2 have been investigated using the first-principles density functional theory calculations.Our results reveal that the volume of codoping systems increases with the increasing atomic radius of metal atoms.The formation energies under different growth conditions have been calculated,showing that the codoping systems are formed easily under O-rich growth conditions.Electronic band structures and density of states have been obtained.The decreased bandgaps,enhanced covalence and appearance of electron acceptors after codoping are all good for p-type conductivity.     

Field-induced magnetic form factor of lutetium

The conduction electron field-induced magnetic form factor of Lu, a rare earth metal with a closed 4f shell, has been measured using the polarized neutron technique. The measurements demonstrate that the conduction electron density is more spatially extended than in the free atom. The experimental results are in good agreement with band calculations of the $\text{spin}$ magnetic form factor.