Ca掺杂ZnO氧化物的电子结构与电性能研究

基于密度泛函理论广义梯度近似第一性原理计算的方法,系统研究了Ca掺杂ZnO氧化物的晶格结构和电子结构,在此基础上分析了其电学性能.结果表明,Ca掺杂ZnO晶胞减小.Ca掺杂氧化物仍为直接带隙半导体材料,带宽达1.5 eV.掺杂体系费米能级附近的能带主要由Cas态、Cap态、Znp态和Op态电子构成,其中p态电子对价带态贡献最大,且Cas态、Znp态和Op态电子之间存在着更强的相互作用.Ca掺杂ZnO氧化物费米能级EF附近载流子浓度增加,运动速度减小,有效质量增加,导电机构为Cas态、Znp态和Op态电子在价带与导带的跃迁,具有更高的电导率,较高的Seebeck系数和综合电性能.     

铁磁态Co基层状氧化物Ca2Co2O5电子状态的研究

采用平面波超软赝势法研究了低自旋状态Co基典型层状氧化物Ca2Co2O5的电子结构.结果表明,层状Co基氧化物Ca2Co2O5呈金属型能带结构,具有明显的各向异性,能带中含有5个子能带,其中费米能附近的能带数量较多,呈较宽的带状分布.自旋向上的电子形成半导体型能带,带隙宽度为0.37 eV,自旋向下的电子形成金属型能带.系统内部的电子对态密度贡献程度依s,p,d依次增大.Ca的电子形成的态密度对费米能附近的值贡献非常小,Co的d态电子对两层态密度贡献较大,其对系统电性能起着重要作用,且系统Co-O之间存在着较强的相互作用.Ca-Co-O层中的各态电子对态密度的贡献大于Co-O层中的各态电子对态密度的贡献.     

C-X(X=Y,Zr)共掺杂SnO2电子结构的第一性原理研究

基于第一性原理方法研究了C单掺杂SnO2和C-X(X=Y,Zr)共掺杂SnO2的能带结构、态密度以及分电荷分布.结果表明:C掺杂、C-Y、C-Zr共掺杂SnO2的带隙值分别为1.109 eV、1.86 eV、1.214 eV,较超胞结构的带隙值降低,有利于电子的跃迁;C-Y共掺杂SnO2的导带底部有3条杂质能级分离出来,C-Zr共掺杂SnO2的能带价带顶部能级中有3条能级分离出来,其中1条能级贯穿费米能级;C-Y,C-Zr共掺杂SnO2的态密度中在低能区会产生1个态密度峰值,部分态密度的峰值由Y、Zr的d轨道贡献;C-Y、C-Zr共掺杂SnO2会打破SnO2电子平衡状态,致使电荷的重新分布.     

掺P石墨烯结构和电子性质的第一性原理研究

基于密度泛函理论第一性原理,在广义梯度近似下,本文研究本征石墨烯和掺杂不同浓度P的石墨烯结构和电子性质并发现本征石墨烯禁带宽度为零;对于P∶C掺杂比分别为1∶17、1∶7、1∶1的石墨烯,其P-C键长由0.142nm的C-C键分别增大为0.1629 nm、0.1625 nm、0.1751 nm,其对应带隙分别由零带隙变为0.28 eV、0.44 eV、1.21eV:费米能级逐渐下降.分析分波态密度后发现,在掺P石墨烯中主要为P原子的3p态电子影响其总态密度.     

电场对氧化镍电子结构的影响

采用超软赝势电子平面波密度泛函理论的方法研究了立方相氧化镍不同外电场下的电子结构.结果表明,立方相氧化镍的晶格参数和对称性保持不变,共价键的成分增强;体系总能在外电场下增大;其间接带隙宽度在外电场下减小.费米能级附近的态密度和电子浓度在外电场下有增大的趋势.电场作用下,立方相氧化镍价带顶的电子有效质量增大,Ni的d态贡献电子能力减弱,O的p态贡献电子能力有所增强,Ni-O结合键强度增大.     

拓扑半金属α2-Ti3Al(0001)表面的电子结构理论研究

采用基于密度泛函理论的第一性原理方法对α2-Ti3Al(0001)表面的电子结构进行计算.结果 表明:(1)α2-Ti3Al(0001)表面的表面能为2.03 J/m2,表面功函数为4.265 eV;(2)表面的总态密度在费米能级处达到极大值,系统呈现金属性,与块体的半金属差异明显,Ti-s、Ti-p和Al-s轨道受层数的影响较小,而Ti-d和Al-p轨道受层数的影响较大,均在费米能级处出现极大值;(3)能带结构未呈现块体的节线环,而是在费米能级附近以下的Γ点,出现一个类电子型的三带交叉点,在费米能级以上的Γ点,出现一个类空穴型的两带交叉点.     

(La,Y)掺杂AlN的电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法对纯AlN、(La,Y)单掺杂以及La-Y共掺杂AlN 超胞进行几何结构优化,计算了稀土元素(La,Y)掺杂前后体系的能带结构、态密度和光学性质。结果表明:未掺杂的AlN是直接带隙半导体,带隙值为E_g=4.237 eV,在费米能级附近,态密度主要由Al-3p、N-2s电子轨道贡献电子,光吸收概率大,能量损失较大;掺杂后使得能带结构性质改变,带隙值降低,能带曲线变密集,总态密度整体下移;在光学性质中,稀土元素掺杂后均提高了静态介电常数、光吸收性能,增强了折射率和反射率,减小了电子吸收光子概率及能量损失;其中La-Y共掺体系变化得较为明显。     

Ni掺杂ZnS的第一性原理计算

采用基于密度泛函理论(DFT)赝势平面波方法计算了ZnS体系Ni掺杂前后的能带结构、态密度和光吸收系数曲线。结果表明:纯ZnS的能带结构是直接带隙,态密度显示属离子性较强而共价键较弱的混合键半导体材料。掺Ni的ZnS禁带宽度随掺杂量增加逐渐减小,能带简并度增大,且向低能方向移动;在价带顶出现杂质能级,说明是p型掺杂。纯ZnS在3.9 eV以下无吸收,红外透过率较高。掺Ni后吸收边红移,且在低能端(绿光区)出现新的吸收峰。     

Mg掺杂浓度对GaN电子结构和光学性质的影响

基于密度泛函理论的第一性原理,分析了Mg掺杂浓度对GaN晶格参数、能带结构、电子态密度和光学性质的影响.研究表明:Mg掺杂GaN体系,晶格常数增大,禁带宽度增加,而且禁带宽度随着Mg含量的增加而增加,同时N2p和Mg2p态电子轨道的相互杂化,从而在费米能级附近引入受主能级,随着Mg含量的增加,费米能级进入价带的位置加深,同时Mg掺杂浓度越高,价带和导带带宽越窄.掺Mg后在介电函数和光学吸收谱的低能区和高能区均出现了新的介电峰,这些峰的出现和禁带中的杂质能级到导带底的跃迁有关,由于带隙的增加使介电峰向高能量方向发生偏移.     

P掺杂6H-SiC的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波法,计算未掺杂与P替换Si、C以及P间隙掺杂6H-SiC的电子结构与光学性质。结果显示未掺杂的6H-SiC是带隙为2.052 eV的间接带隙半导体,P替换Si、C掺杂以及P间隙掺杂6H-SiC带隙均减小,分别为1.787 eV、1.446 eV和0.075 eV,其中P间隙掺杂带隙减小幅度最大。P替换掺杂6H-SiC使得费米能级向导带移动并插入导带中,呈n型半导体。P间隙掺杂价带中的一条能级跨入费米能级,因此在禁带中出现一条P 3p杂质能级,P间隙掺杂6H-SiC转为p型半导体。替换与间隙掺杂使得6H-SiC的介电函数实部增大,介电函数虚部、吸收光谱、反射光谱与光电导率红移,其中P间隙掺杂效果最佳。通过P掺杂材料的电导率增强,对红外波段的利用率明显提高,为6H-SiC在红外光电性能方面的应用提供有效的理论依据。     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.