准晶介绍

什么是准晶？为什么谢赫特曼在1982年4月的发现会被如此的不相信,而且需要花费2年半的时间才能在科学文献中找到它？为什么5重对称性的首次被发现会引起如此的大惊小怪？我们说晶体有这种对称性实际意味着什么？在我们回答上述问题之前,让我们先回顾一下其的某些背景。几个世纪以来,晶体都只被看作是有平坦的表面（小平面（facets...     

MB25镁合金中的准晶体与晶体相的研究

利用透射电子显微术（ＴＥＭ）及能谱仪微区成分分析（ＥＤＳ）技术，对含有稀土元素的铸态Ｍｇ－Ｚｎ－Ｚｒ－Ｙ系高强镁合金ＭＢ２５中的稀土相鉴定发现，在铸态合金的晶界上存在准晶相，其电子衍射谱显示出５－３－２次对称的特点，为二十面体准晶相。在与准晶相连区域发现一种ＭｇＺｎ＿２型的Ｌａｖｅｓ相，其点阵常数为ａ＝０．５４２ｎｍ，Ｃ＝０．８７３ｎｍ。     

准晶体的结构化学

介绍准晶体的历史、结构、对称性和性质,介绍Mg32(Al,Zn)49的晶体结构和对称性,同时讨论纳米准晶颗粒的制备方法及其应用。     

准晶简述——2011年度诺贝尔化学奖

2011年诺贝尔化学奖颁发给了以色列科学家DanShechtman,以表彰他在准晶发现上的突出贡献。本文简单介绍准晶发现的重要意义及其结构的描述方式。     

晶体的五次旋转对称

晶体结构的两大特征——长程平移有序和长程取向有序分开时,可能产生5次或其它非经典轴次旋转对称.5次旋转对称与准周期点阵有关.     

多羟基化合物法制备五次孪晶银纳米线的生长机理

运用多羟基化合物方法, 在添加表面活性剂聚乙烯吡咯烷酮(PVP) K30的溶液中合成了多次孪晶银纳米颗粒和纳米线. 运用透射电子显微术(TEM)和光吸收谱, 对不同的摩尔比n(PVP):n(AgNO3)和不同的搅拌条件下制备的纳米线进行了对比研究. 结果表明, 这种方法的制备过程中不仅存在由五个{111}面包裹成的锥形生长, 而且还同时存在垂直于生长方向的{110}层状生长, 并且两者之间还存在着竞争; 另外对纳米线的弯折处进行的高分辨电子显微学研究表明, 纳米线制备过程中遭受的塑性变形在纳米线中产生了大量的层错和位错; 纳米线折断产生的新鲜断口容易成为新的晶粒形核位置.     

碲化镓纳米片中单斜晶相和六方晶相共存的光谱特征（英文）

快速发展的二维层状材料为构建新型高效的微纳发光器件和光电探测器件提供了新的平台.其中碲化镓纳米片备受关注,这是因为碲化镓从少层到块体都具有极强的发光性能,因而可以降低二维微纳器件的制备条件.然而碲化镓纳米片具有单斜和六方等多种晶相,使其发光特性和光谱结构异常复杂,目前还缺少对不同厚度碲化镓纳米片荧光光谱的系统研究.本文研究了不同厚度碲化镓纳米片的荧光光谱和拉曼光谱,以及荧光光谱从低温(4 K)到室温的演化行为.通过光谱分析,发现单斜晶相和六方晶相可能同时共存于多层碲化镓纳米片中.为了阐述相关实验结果,构建了如下原子结构模型:其中六方晶相位于纳米片的顶层与底层,而单斜晶相位于纳米片的中间位置.基于温度依赖的荧光光谱,可以获得六方晶相的光学带隙为1.849 eV,且该激子峰只能在较高温度(>200 K)下和声子辅助下才能表现出显著的荧光发射行为.进一步的实验结果确定了六方晶相的激子-声子相互作用强度约为1.24 meV/K.本工作证实了碲化镓纳米片中单斜晶相与六方晶相共存的实验现象,为研究碲化镓纳米片的晶相变化和激子动力学,以及探究碲化镓的奇异物理化学特性,提供了新的见解.     

烷基胺为媒介的铜纳米棒的合成及其生长机制研究

以氯化铜为前躯体,葡糖糖为还原剂,烷基胺(十六胺和十八胺的混合物)为络合剂和表面包覆剂,经过络合反应和溶剂热两步反应首先得到形貌均一、直径约为100 nm的铜纳米颗粒, 随后自发生长为五重孪晶铜纳米棒(仍含有部分颗粒)。实验过程中分别对溶剂热反应1 h、3 h和5 h后的还原产物的形貌特征加以表征,可以推断被还原的铜原子首先均匀成核形成初级铜纳米颗粒,经过奥斯特瓦尔德老化过程生长为五重孪晶的次级铜纳米颗粒,由于孪晶结构具有很高的生长活性,在烷基胺的表面包覆作用下生长为各项异性的铜纳米棒。该方法提供了一种有效的铜纳米棒的制备方法并且降低了一维铜纳米材料的合成成本。     

二十面体准晶对非晶形成影响的模拟

采用分子动力学模拟技术,以液态金属Ni为例,研究了在不同冷却条件下形成晶体及非晶的过程.模拟采用镶嵌原子法(EAM)作用势,得到了不同温度、不同冷却速度下Ni的径向分布函数以及原子组态变化的重要信息,利用键对分析技术探讨了二十面体准晶对非晶形成的影响.     

DEDUCTION OF QUASILATTICE WITH FIVE-FOLD SYMMETRY AND PARTICLE FRACTAL STRUCTURE MODEL

In the structure of quasicrystal, the coordination icosahedron has long ordering but no translation ordering. The author dealt with the building principle ofquasicrystal and thought that two principles played a certain role in the quasicrystal structure, i.e. the icosahedron principle and the golden mean principle. We obtained the most simple.structure model of quasicrystals, and could explain all details of the high-resolution electron microscopic image of the A1-Mn quasicrystal based on the two principles. The author's model has the characteristic of fractal structure, therefore, we call it the particle fractal structure madeh The author has made a systematic deduction of quasicrystal point group, forms, possible type of quasicrystal lattice.     

A Crystallographic Investigation of Ergolines

The X-ray crystal structures of three ergoline derivatives have been completed and are reported herein. These include mesulergine hydrochloride (III), pergolide methanesulfonate (IV), and dihydroergocriptine hydrate (V). These molecules show dopamine agonist activity at the D2 receptor. These three-dimensional structures were compared to structurally similar molecules with similar pharmacological activity. It was found that ergoline derivatives have rigid fused-ring systems with substituents that can exist in a variety of conformations. The ergoline structures reported here have structural features consistent with other active dopamine agonists. Crystallographic data: (III) C₁₈H₂₆N₄O₂S HCl, monoclinic space group P2₁, a = 12.183(2) Å, b = 6.174(2) Å, c = 13.649(2) Å, = 105.55(1)°, Z = 2, final R = 0.071 for 2293 observed reflections [I > 3(I)]; (IV) C₁₉H₂₇N₂S CH₃SO₃, mono- clinic space group P2₁, a = 8.455(4) Å, b = 29.868(4) Å, c = 8.957(6) Å, = 111.95(5)°, Z = 4, final R = 0.055 for 3836 observed reflections; (V) C₃₂H₄₃N₅O₅ H₂O, monoclinic space group P2₁, a = 12.403(2) Å, b = 18.103(3) Å, c = 15.418(3) Å, = 113.04(2)°, Z = 4, final R = 0.058 for 3208 observed reflections.     

Crystallographic investigation of the Co-B-O system

The crystalline phases within the Co-B-O system have been investigated with a combination of powder and single crystal X-ray diffraction. By varying the synthetic conditions, four pure phases can be made by solid-state reaction: Co₃(BO₃)O₂, a homometallic ludwigite; Co₃(BO₃)₂, an orthoborate with the kotoite structure; Co₂(B₂O₅), a pyroborate; and the tetraborate Co(B₄O₇). Herein, we report the first structural refinement of the latter phase (orthorhombic, space group Pbca, a=8.1189(7) Å, b=8.621(1) Å, c=13.737(1) Å, V=961.5(2) Å³, Z=8, R₁=0.0319, wR₂=0.0693 [I>2σ(I)]). The pyroborate structure was also refined by single crystal methods in order to match the calculated powder diffraction pattern with the observed pattern (triclinic, space group , a=3.1689(3) Å, b=6.1530(5) Å, c=9.2734(7) Å, α=104.253(4)°, β=90.821(4)°, γ=92.098(5)°, V=175.08(3) Å³, Z=2, R₁=0.0159, wR₂=0.0366 [I>2σ(I)]). Flux growth of Co(B₄O₇) also yielded single crystals of the new compound Co₄(BO₂)₆O (cubic, space group , a=7.4825(3) Å, V=418.93(3) Å³, Z=2, R₁=0.0176, wR₂=0.0373 [I>2σ(I)]).     

Eye‐Catching Dual‐Fluorescent Dynamic Metal–Organic Framework Senses Traces of Water: Experimental Findings and Theoretical Correlation

A guest‐dependent dynamic fivefold interpenetrated 3D porous metal–organic framework (MOF) of Zn^II ions has been synthesized that exhibits selective carbon dioxide adsorption. Furthermore, the MOF shows excellent luminescence behavior, which is supported by a systematic study on the guest‐responsive multicolor emission of a suspension of the MOF. The dual‐emission behavior arises from the excited‐state intramolecular proton transfer (ESIPT), and the compound also shows remarkable potential to detect traces of water in various organic solvents. The experimental observations were also painstakingly authenticated by using time‐dependent density‐functional‐theory (DFT) calculations.     

Application of 2-point Padé approximants to the ground state of the 2-dimensional hydrogen atom in an external magnetic field

The 2-dimensional hydrogen atom in an external field r ² is important in certain problems of solid-state physics. The exact results for the ground state are obtained from the numerical solution of the radial Schrödinger equation and are compared with various 2-point Padé approximants. Terms to order ⁴ in the low-field RS expansion are combined with 5 terms in the high-field expansion in order to obtain the Padé approximants. The results indicate that the best approximants have relative errors in the range 10^–8 to 10^–5 throughout the interval = 0 4.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday