Classifying crystal structures

Common usage has now defined a system for naming crystal structure types of intermetallic phases—but we still need a few arbitrary rules.     

Synthesis,crystal structures and properties of new radical cation salts based on some tetrathiapentalene derivatives with halogenomercurate anions

New radical cation salts of BDH-TTP [2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene], BDA-TTP [2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] and DTDH-TTP [2-(1,3-dithiol-2-ylidene)-5-(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene] with halogenomercurate anions have been prepared. X-ray analysis at 120 K revealed the κ-type arrangement of conducting donor layers in (BDH-TTP)₄Hg₃Br₈ and (BDH-TTP)₄Hg₃Cl₈, and the β-type packing of donor layers in the (BDA-TTP)₄Hg₂Br₆, (BDA-TTP)₆Hg₄I_10.34 and (DTDH-TTP)₆Hg₃Br₉ radical cation salts. The crystals of κ-(BDH-TTP)₄Hg₃Br₈, κ-(BDH-TTP)₄Hg₃Cl₈ and β-(DTDH-TTP)₆Hg₃Br₉ behave as metals down to liquid helium temperatures, the resistivity of BDA-TTP salts shows semiconducting temperature dependence.     

钛-氢体系晶体结构和能量的第一原理计算

采用基于密度泛函理论的第一原理赝势平面波方法研究了不同钛一氢摩尔比的α-Ti-H和声．Ti-H晶体的稳态几何结构,进行了稳态晶体的总能量计算。结果表明：氢引起α-Ti和β-Ti晶格点阵畸变,晶体体积膨胀。计算得到的不同钛一氢摩尔比的α-Ti-H和β-Ti-H晶体结合能分别小于α-Ti和β-Ti晶体结合能,表明氢原子降低了α-Ti和伊Ti晶体的结合能。氢原子在β-Ti晶体中的占位随氢含量变化,低氢含量时易占据四面体间隙位置,高氢含量时倾向于占据八面体间隙位置。     

Synthesis, crystal structure and properties of two ternary rare earth complexes with aromatic acid and 1,10-phenanthroline

Two dimeric rare-earth complexes [Eu(o-MOBA)₃phen]₂·2H₂O (1), [Tb(o-MOBA)₃phen]₂·2H₂O (2), (where o-MOBA = o-methoxybenzoate, phen = 1,10-phenanthroline) were synthesized and structurally characterized. Both of them consist of neutral dimeric molecules, crystallize in triclinic system, space group P. Each RE(III) ion is nine-coordinated with one 1,10-phenanthroline molecule, one bidentate chelating carboxylate group, two bidentate bridging carboxylate groups and two tridentate bridging carboxylate groups. Complex 1 shows bright red luminescence, 2 shows green luminescence under UV light at room temperature, respectively. The thermal analysis indicates that they are all quite stable to heat.     

High-pressure synthesis and crystal structures of two new polyphosphides, NaP5 and CeP5

Two novel polyphosphides, NaP₅ and CeP₅, were prepared in a BN crucible by the reaction of elemental components under a high pressure of 3 GPa at 800–950 °C. The X-ray structural analysis showed that NaP₅ crystallizes in an orthorhombic space group Pnma with a=10.993(2) Å, b=6.524(1) Å, c=6.903(1) Å, Z=4 and CeP₅ in the monoclinic group P2₁/m with a=4.9143(5) Å, b=9.6226(8) Å, c=5.5152(4) Å, β=104.303(6)°, Z=2. The crystal structure of NaP₅ consists of a three-dimensional framework _∞³[P₅]¹⁻ constructed by P---P bonds among four crystallographically inequivalent phosphorus sites, with large channels hosting the sodium cations, while CeP₅ is a layered compound containing _∞²[P₅]³⁻ polyanionic layers that are separated by Ce³⁺ ions. NaP₅ exhibits the diamagnetic behavior, while the temperature-dependent magnetic susceptibility of CeP₅ essentially follows the Curie–Weiss law.     

The centennial of the first X-ray crystal structures

A short account is given of the discoveries of the first crystal structures using X-ray diffraction by William Henry Bragg and William Lawrence Bragg, a father and son team working at Leeds University and Cambridge University. Their first publications, separately and together, are highlighted. This is a contribution to the centennial celebrations of these discoveries and looking towards the International Year of Crystallography to be celebrated in 2014 led by the International Union of Crystallography.     

Identifying close-packed planes in complex crystal structures

It is often necessary to identify close-packed or nearly close-packed planes in a crystal. This can be done by inspection in crystal structures where one atom occupies each lattice point – i.e. face-centred cubic and body-centred cubic crystals. However, in more complex crystal structures intuitive inspection becomes rather difficult. The present paper describes a simple method for identifying close-packed or nearly close-packed planes in crystals containing more than one atom per lattice point. The method also distinguishes between “flat” planes, where all the atom centres lie in the plane, and “rumpled” planes, where the atom centres do not lie in the plane. The extent of the departure from true “flatness” can also be estimated.     

金属纳米微粒晶体结构的稳定性及其结合能

建立了金属纳米微粒的结合能模型,该模型以微粒尺寸、形状因子和密堆因子为主要参数.根据该模型计算V、Cr、Nb、Mo、Ta、W和Fe元素纳米微粒的结合能.结果表明:一定形状下,在一定的临界尺寸时各纳米微粒bee结构的结合能和fcc结构的结合能相等:当微粒尺寸大于该临界尺寸时,bcc结构更稳定,小于该尺寸时,fcc结构更稳定.进一步的计算表明,球形和正四面体形可以看作近正多面体形的两个极限,多面体形微粒发生结构转变的临界尺寸介于两个极限尺寸之间,与文献中报道的结果一致.     

Modeling fluid flow in three-dimensional single crystal dendritic structures

Convection during directional solidification can cause defects such as freckles and misoriented grains. To gain a better understanding of conditions associated with the onset of convective instabilities, flow was investigated using three-dimensional (3D) computational fluid dynamics simulations in an experimentally obtained dendritic network. A serial-sectioned, 3D data set of directionally solidified nickel-base superalloy measuring 2.3 × 2.3 × 1.5 mm was used to determine the permeability for flow parallel and normal to the solidification direction as a function of solid fraction (f_S). Anisotropy of permeability varies significantly from 0.4 < f_S < 0.6. High flow velocity channels exhibit spacings commensurate with primary dendrite arms at the base of the mushy zone but rapidly increase by a factor of three to four towards dendrite tips. Permeability is strongly dependent on interfacial surface area, which reaches a maximum at f_S = 0.65. Results from the 3D simulation are also compared with empirical permeability models, and the microstructural origins of departures from these models are discussed.     

Diamine ligands with multiple coplanar conjugation rings and their phosphorescent copper complexes: Synthesis,characterization, crystal structures,and photophysical property

In this paper, we report a series of diamine ligands with multiple coplanar conjugation rings and their corresponding phosphorescent Cu(I) complexes, including their synthesis, crystal structures, photophysical properties, and electronic nature. Geometric parameters suggest that the Cu(I) center localizes at a distorted tetrahedral geometry within the Cu(I) complexes. Theoretical calculation reveals that all emissions originate from triplet metal-to-ligand-charge-transfer excited state. It is found that the free rotation of conjugation rings may compromise the coplanar plane and thus has little effect on the photophysical property of their corresponding Cu(I) complexes. But excess coplanar conjugation moiety is harmful for emissive state. The detailed quenching mechanism is investigated.     

Synthesis of polythienylenevinylene copolymers bearing carbondithioate structures

A new type of thiophene-based copolymers bearing the carbondithioate groups were synthesized through Wittig–Horner reaction. Copolymers were characterized by elemental analysis, UV–Vis, and FT-IR. Conductivity of I₂ doped copolymers ranges from 10⁻³ to 10⁻² S/cm.     

Arthur Lindo Patterson,his function and element preferences in early crystal structures

In 1934, Arthur Lindo Patterson showed that a map of interatomic vectors is obtainable from measured X-ray diffraction data without phase information. Such maps were interpretable for simple crystal structures, but proliferation and overlapping of peaks caused confusion as the number of atoms increased. Since the peak height of a vector between two particular atoms is related to the product of their atomic numbers, a complicated structure could effectively be reduced to a simple one by including just a few ‘heavy’ atoms (of high atomic number) since their interatomic vectors would stand out from the general clutter. Once located, these atoms provide approximate phases for Fourier syntheses that reveal the locations of additional atoms. Surveys of small-molecule structures in the Cambridge Structural Database during the periods 1936–1969, when Patterson methods were commonly used, and 1980–2013, dominated by direct methods, demonstrate large differences in the abundance of certain elements. The ‘moderately heavy’ elements K, Rb, As and Br are the heaviest elements in the structure more than 3 times as often in the early period than in the recent period. Examples are given of three triumphs of the heavy atom method and two initial failures that had to be overcome.     

原始组织对高温合金热处理组织和力学性能的影响

对具有不同枝晶间距的CMSX 2单晶高温合金的凝固组织特征及其对热处理组织和持久性能的影响进行了研究。考察了不同温度下不同枝晶间距组织的固溶情况及热处理后的组织均匀性 ,测试了持久性能。结果表明 :随着凝固组织的细化 ,合金的组织均匀性得到提高 ,从而有效提高了合金的固溶温度 ,增大了热处理均匀化效果 ;CMSX 2合金铸态超细组织单晶的持久寿命是粗枝晶单晶的 1.4 5倍 ,热处理态超细枝晶单晶的持久寿命是粗枝晶单晶的 1.85倍。单晶高温合金组织超细化是显著提高合金高温力学性能的有效手段     

电子束照射下纳米TiO2晶型转变的高分辨透射电镜原位观察

使用场发射透射电镜及其扫描透射装置(STEM)和高角环形暗场像(HAADF)装置及EDS能谱仪研究了溶胶凝胶法制备的TiO2纳米微粒在电子束照射下晶体结构发生变化的现象,在200kV电子束照射下,经过不同时间的原位观察发现,纳米TiO2颗粒由开始的体心正方141/amd(141)锐钛矿TiO2晶型转变为非晶体,随后又在电子束的照射下晶化为简单正方P42/mnm(136)金红石TiO2单晶,随后转变为尺寸更小的金红石TiO2纳米多晶体.HADDF图可以看到最后的晶粒细化过程中,原子有选择的进行迁移,使晶化区域的样品厚度不均匀化,能谱分析证明样品中只有TiO2存在.     

Synthesis of highly-oriented polyacetylene film in a liquid crystal solvent

The synthesis of oriented polyacetylene films is investigated by using a nematic liquid crystal as polymerization solvent. Highly-oriented thin films are obtained under a flow of catalyst solution in which a nematic liquid crystal is used instead of common solvents such as hexane and toluene. Nematic liquid crystals that could be used as solvents for the Ziegler-Natta catalysts are limited due to their reactive substituents with the active species and/or the components of the catalyst. Among the available nematic liquid crystals, phenylcyclohexane type is stable in the presence of Ziegler-Natta catalysts. Since fibril alignment in the oriented films is found to be along the flow direction of the catalyst solution, it appears that the direction of fibril growth coincides with that of the liquid crystal orientation, which is caused by an alignment effect of the liquid crystal molecules under a flow of the solution.This new and simple method allows quite large highly-oriented films to be synthesized, which makes it possible to investigate various kinds of anisotropic properties of polyacetylene.