Y,Zr,Nb掺杂对单层MoS2电子结构的影响

本文基于第一性原理的方法研究了Y、Zr、Nb在Mo位掺杂单层MoS2的能带结构和态密度.研究发现:Y、Zr、Nb三种杂质在Mo位掺杂使杂质原子附近的键长发生畸变,畸变最大的是Y掺杂体系;Y、Zr、Nb的掺杂改变了单层MoS2能能带结构,使掺杂体系向导体转变;对于Y、Zr、Nb共掺杂体系,Y、Zr共掺杂增强了单层MoS2导电性能;Y、Nb共掺杂单层MoS2的费米能级穿过杂质能级,此处的能级处于半满状态,容易成为电子的俘获中心;Zr、Nb共掺杂体系的禁带中出现了多条杂质能级,同时导带能量上移;Y、Zr、Nb共掺杂可以很大程度改变单层MoS2材料的电子结构.     

Li-O共掺杂AlN晶体的第一性原理研究

采用基于密度泛函理论的第一性原理全势线性缀加平面波法,研究了Li-O共掺杂纤锌矿AlN体系的品格结构、电子态密度、能带结构和光学性质,较详细地分析了O对Li掺杂AlN晶体p型特性的影响.结果表明:Li-O共掺杂会导致AlN晶格收缩和禁带宽度减小;与Li单掺杂相比,O杂质的加入使得价带顶部的态密度峰值减小且局域化加强,降低了Li在AlN晶体中的受主特性.相较于未掺杂时的情况,Li-O共掺杂AlN的介电函数虚部谱只保留了位于7.5 eV处的主峰,谱线也变得更加平缓,而材料的吸收区范围未受到影响.Li-O共掺杂后的AlN材料依然能很好地工作在紫外光区域.     

La-W共掺杂对AgSnO2触头材料热性能影响的仿真分析

针对目前较少有学者通过共掺杂其他元素对AgSnO2触头热性能进行研究的现状.采用对SnO2晶体进行非掺、单掺La和共掺La-W元素的方法,通过密度泛函理论、第一性原理以及CASTEP软件对掺杂体系的热学性质进行理论计算,得到了不同掺杂情况下SnO2晶体的声子谱、声子态密度及分波态密度和相关热力学参量,对计算结果和曲线图进行了理论分析.结果 表明:当掺杂浓度为16.67;时,共掺杂La-W元素的SnO2体系声子谱未出现虚频,而单掺La元素体系出现了虚频,说明共掺杂体系较稳定.通过分析态密度图及分波态密度图可以得到,W原子混合掺杂后可有效改善La原子的振动情况.通过SnO2晶体热力学性质的分析,共掺杂后体系的熵、自由能以及焓的曲线有较好改善,为AgSnO2触头材料在恶劣环境下受到损害后恢复到原状提供了有利条件.且掺杂后晶体的热容明显大于未掺杂晶体的热容,说明La-W元素的掺杂极大的激活了分子的运动活性.     

In掺杂对MVB-Te溶剂法生长的ZnTe晶体光电性能的影响

采用Te溶剂结合改进的垂直布里奇曼法(MVB)制备了In:ZnTe与ZnTe晶体,并对晶体的光学与电学特性进行了表征.通过红外透过显微成像技术观察了In:ZnTe与ZnTe中的Te夹杂并进行了统计分析,发现In掺杂未对ZnTe中的Te夹杂的分布和尺寸产生显著影响.红外透过光谱分析表明,In:ZnTe与ZnTe晶体的红外透过率曲线均表现出平直的趋势,且其平均透过率基本相等,约为60;,进一步表明In的掺入并未导致严重的晶格和杂质吸收.然而,Ⅰ-Ⅴ测试分析发现,In掺杂使得ZnTe晶体的电阻率提高了5个数量级.同时Hall测试分析表明,In:ZnTe与ZnTe晶体均为p型导电,In掺杂很大程度上补偿了晶体中的Vzn,使得晶体中的载流子浓度降低了4个数量级.对比了两种晶体的紫外-可见-近红外透过光谱,可以观察到,In掺杂使ZnTe的吸收边从550 nm红移到560nm,这可能是由于In掺杂引入的浅能级导致的吸收边带尾现象造成的.     

Ni2+对KDP晶体生长及缺陷影响的研究

采用传统降温方法生长了不同Ni2+掺杂浓度的KDP晶体.实验发现当Ni2+掺杂浓度小于1000 ppm时溶液的稳定性随着掺杂浓度的增加而提高,大于1000 ppm时溶液的稳定性开始下降,但仍高于纯态溶液的稳定性;随着Ni2+浓度的增加KDP晶体柱面的生长死区增加,柱面的生长速度略有下降,但在生长过程中没有观察到晶体的楔化;KDP晶体的XRD分析及缺陷的研究表明Ni2+对晶体的结构影响不明显,但晶体中的缺陷和内应力增加.     

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。     

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.     

不同价态稀土元素Eu掺杂锐钛矿相TiO2的电子结构及光学性质

基于密度泛函理论(DFT)的第一性原理的平面波超软赝势法对锐钛矿TiO2晶体和Eu3+,Eu2分别掺杂的锐钛矿TiO2晶体的晶格参数、能带结构、态密度、差分电荷密度以及吸收光谱进行了计算.结果表明:不同价态Eu掺杂后锐钛矿TiO2晶胞膨胀,晶格都发生畸变;同时引入了杂质能级,减小了锐钛矿相TiO2的禁带宽度,TiO2的光吸收带边发生明显红移,在紫外区和可见光区的吸收系数增大.     

Sb-Na共掺p型ZnO的第一性原理研究

运用密度泛函理论,计算了Sbzn、Nazn、Sbzn-nNazn掺杂ZnO晶体的稳定性、能带结构和电子态密度.研究发现Sbzn、Nazn、Sbzn-nNazn掺杂ZnO晶体的结构稳定,Sb-Na共掺杂改善了体系的固溶度.能带结构表明,SbZn体系为n型间接带隙半导体材料;NaZn、Sbzn-2NaZn体系为p型半导体材料;Sbzn-NaZn、SbZn-3NaZn体系为本征半导体材料.对p型半导体材料体系的导电性能研究发现,Sbzn-2Nazn体系电导率大于NaZn体系的电导率,即Sbzn-2NaZn掺杂改善了体系的导电性.计算结果为实验制备p型ZnO材料提供了理论指导.     

Cu替位与空位及Cu、S共掺SnO2的光磁性质研究

运用第一性原理,基于密度泛函理论,计算了Cu分别以替位和空位两种方式掺杂SnO2的电子结构和光电特性,并对两种掺杂方式做了一定的比较研究;磁性方面,主要研究了Cu、S共掺SnO2后的磁学性能.计算表明,两种方式掺杂,都使SnO2具有半金属特性,Cu原子将与周围的O原子发生强烈的交换作用,Cu原子对态密度的贡献主要在费米能级附近.相比之下,空位掺杂后的晶胞体积略大于替位掺杂后的SnO2,对光的能量损耗也比替位掺杂的低.对于Cu、S共掺的体系,计算表明:每个Cu原子的掺入将产生0.46μB的磁矩,而一个S原子将引入0.36μB的磁矩,Cu原子周围的O原子也对磁矩有一定的贡献.经过分析,发现体系的磁性来源主要是Cu-3d和S-3p,以及Cu-3 d与O-2 p间的强烈耦合作用.     

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.     

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.     

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.     

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.