A new method for the investigation of orientation relationships in meteoritic plessite

The orientation relationship (OR) between the bcc and fcc phase in the plessite microstructure of the iron meteorites Watson, Agpalilik and Gibeon has been analysed in a scanning electron microscope using electron back‐scattered diffraction (EBSD). A very strong OR exists, independently on the analysed plessite type and the observed spreading of single orientation data. The agreement between the experimental orientation distribution and existing models varies for each meteorite. The black plessite in the Agpalilik corresponds to the Nishiyama‐Wassermann model whereas the duplex plessite of the Gibeon meteorite shows an OR close to the Kurdjumov‐Sachs model. The Watson meteorite is strongly deformed so that a general OR is difficult to determine due to the blurred experimental orientation distribution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the capability of revealing the pseudosymmetry of the chalcopyrite‐type crystal structure

The tetragonal crystal‐structure type of chalcopyrites (chemical formula A^IB^IIIC^VI₂) is a superstructure of sphalerite type. The c /a ratio differs generally from the ideal value 2, i.e., the crystal structure is pseudocubically distorted. For CuInSe₂ and CuGaSe₂ thin films, simulations demonstrate that it is theoretically possible to reveal the tetragonality in electron backscatter‐diffraction (EBSD) patterns for CuGaSe₂, whereas it may not be possible for CuInSe₂. EBSD experiments on CuGaSe₂ thin films using the ”Advanced Fit” band‐detection method show that it is possible to extract accurate misorientation‐angle distributions from the CuGaSe₂ thin film. Pole figures revealing the texture of the CuGaSe₂ thin film are shown, which agree well with X‐ray texture measurements from the same layer. (© 2008 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved determination of fcc/bcc orientation relationships by use of high‐indexed pole figures

The use of variants to analyze fcc/bcc orientation relationships is demonstrated by EBSD data. Because of multiply occupied poles in the stereographic projections low indexed pole figures are not always suitable. This is mostly caused by the convolution of all scattered individual orientation data as the single poles cannot resolved in the pole figure. Pole figures of higher indexed lattice planes more reliably reflect the character of the orientation relationship since no overlapping of poles occurs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Diffusion Anisotropy of Polycrystals

A model of diffusion anisotropy appearance in a textured polycrystalline aggregate under the grain boundary diffusion preponderance (the C type of kinetic) has been suggested. Although in the textured polycrystal there exists a distribution over 5 degrees of freedom describing the grain boundaries macroscopically, it is the misorientation distribution that has been shown to may give rise to the diffusion anisotropy. Presence of small-angle boundaries and a certain, sufficiently sharp texture is the key moment at this.     

Synchrotron White Beam X-Ray Topography Characterization of Defect Structures in 2,10-Undecanedione/Urea Inclusion Compounds

Abstract

The defect structure of a crystal of the urea inclusion compound (UIC) of 2,10-undecanedione was investigated using Synchrotron White Beam X-ray Topography. X-ray transmission topographs recorded from different regions show that the crystal is divided into several twin domains. Each region in the crystal is revealed on the topographs by orientation contrast arising from the mutual misorientation of adjacent regions. Using a combination of pinhole Laue pattern analysis and topographic orientation contrast analysis, the twin operation was determined to be consistent with an approximately 60° rotation about the orthorhombic c-axis. Possible twin boundary structures are also presented. Other defects such as dislocations and inclusions are also characterized.     

Growth and structural characterization of [ZnL(DMSO)]

A novel mononuclear zinc(II) complex [ZnL(DMSO)] (1) with chelating bisoxime ligand 4,4′‐dinitro‐2,2′‐[ethylenedioxybis(nitrilomethylidyne)]diphenol (H₂L) was synthesized and structurally characterized by X‐ray crystallography. The complex crystallizes in the triclinic system, space group P‐1, with unit cell parameters a = 8.9730(16), b = 11.9080(18), c = 20.701(2) Å, α = 103.893(3), β = 101.975(3), γ = 90.029(2) and Z = 4. The Zinc(II) ion is five‐coordinated by four N₂O₂ donor atoms of L^2‐ and one oxygen atom from DMSO molecule. Interestingly, the unit of cell contains two crystallographically independent but chemically identical mononuclear complexes. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and structure of a new one‐dimensional cobalt complex with dicyanamide and 4‐picolyl choride bridges

The synthesis and structure of the 1D cobalt (II) complex, [Co( L )₂(dca)₂] ( 1 ) (dca = dicyanamide, C₂N₃^–, L = 4‐picolyl choride) is reported. Complex 1 crystallized in triclinic system, space group P ‐1, with cell dimensions of a = 7.291(2) Å, b = 7.481(2) Å, c = 9.007(3) Å, α =104.444(4)°, β = 96.971(4)°, γ =102.618(4)°, V = 456.1(2) ų, Z = 1, Dc = 1.624 Mg/m³. In complex 1 , Co (II) is 6‐coordinated by N atoms of four dca ligands and two L ligands. The centrosymmetric CoN6 chromophore is an axially elongated octahedron that has Co‐N distances ranging from 2.122(3) to 2.154(3) Å. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Syntheses and crystal structures of two polymorphs of three‐dimensional silver (I) 5‐(3‐aminophenyl)tetrazolates

Two polymorphs of silver 5‐(3‐aminophenyl)tetrazolates – α‐ and β‐Ag(amphttz) have been obtained by the reaction of amphttzH with AgNO₃ in presence of ammonia either in ambient condition or under the hydrothermal condition, respectively (amphttzH = 5‐(3‐aminophenyl)tetrazole). Both of the two phases of Ag(amphttz) were characterized by elemental analyses, IR spectra and single‐crystal X‐ray diffraction. X‐ray analysis shows α‐, β‐phases crystallize in P ‐1 with a = 8.551 (2) Å, b = 8.720(2) Å, c = 11.173(2) Å, α = 98.15(3)°, β = 90.95(3)°, γ = 95.45(3)° and C 2/c with a = 13.542(3) Å, b = 10.135(2) Å, c = 12.610(3) Å, β = 113.58(3)°, respectively. The two polymorphs exhibit different 3D structures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology of silver bromide crystals produced at presence of N,N ‐dimethylformamide

The study deals with examination of conditions that are necessary to obtain flat crystals of silver bromide that grow in a water and gelatine crystallization environment where N,N ‐dimethylformamide is used as the agent that is conducive to complexing of sparingly soluble silver bromide. The examination focused on the issue how changes in volumetric concentration of N,N ‐dimethylformamide as well as concentration of excessive ions of silver bromide in the dispersive solution affect morphology and size of newly created of silver bromide. The completed experiments enabled to determine boundary limits of both N,N ‐dimethylformamide and bromide ions concentration where suspensions of silver bromide crystals exhibit predominant content of triangular, transient and hexagonal flat forms with very high aspect ratio. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

MAEAM investigation of the structural stability and theoretical strength of Fe crystals under uniaxial loading

The structural stability and theoretical strength of BCC crystal Fe under uniaxial loading have been investigated with the modified analytic embedded‐atom method (MAEAM). Even if an orthorhombic path is applied, the deformation is spontaneous along the tetragonal path till Milstein modified Born criterion B₂₂‐B₂₃>0 is violated at λ₁=0.9064 in the compressive region. The branched orthogonal path with lower compressive stress σ₁ and energy E is preferred over the conventional tetragonal Bain path. A stress‐free FCC phase with the local maximum energy of ‐4.2186eV appearing either in compressive region (orthorhombic path) at λ₁=0.8923 or in tensile region (tetragonal path) at λ₁=1.2619 is unstable and would slip spontaneously into its near neighbor stress‐free mBCT phase with the local minimum energy of ‐4.2270eV. The initial BCC phase with the lowest energy of ‐4.280eV is the most stable in correspondence with the actual behavior of Fe. Furthermore, the stable region ranges from ‐79.7eV/nm³ to 30.6eV/nm³ in the theoretical strength or from 0.9064 to 1.1788 in the stretch λ₁ correspondingly. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effective electro‐optic coefficient of (1–x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

Refractive indices and effective electro‐optic coefficient γ_c of (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PZN‐xPT, x = 0.05, 0.09 and 0.12) single crystals were measured at 532 nm wavelength. Orientation and temperature dependences of the electro‐optic coefficient were investigated. Large electro‐optic coefficient (γ_c = 470 pm/V) was observed in [001]‐poled PZN‐0.09PT crystal. More importantly, γ_c of tetragonal PZN‐0.12PT is almost unchanged in a temperature range −20 ∼ 80 °C. The γ_c of PZN‐xPT single crystals are much higher than that of widely used electro‐optic crystal LiNbO₃ (γ_c = 20 pm/V). These results show that PZN‐xPT single crystals are very promising materials for electro‐optic modulators in optical communications.     

The structural response of BCC Fe lattice loaded in [110] direction

The structural response of BCC Fe lattice loaded in [110] direction has been investigated with MAEAM. The results show that, even if an orthorhombic path (b₂≠b₃) is applied, the deformation is spontaneous along the tetragonal path (b₂≡b₃) while b₁ is less than 0.3449nm in compressive region. In addition to the initial BCC phase, a BCT phase and the other BCC phase appear also at stress‐free states. The BCT phase with the local maximum internal energy of ‐4.227eV is unstable and would slip spontaneously into the appeared BCC phase with the same minimum internal energy of ‐4.280eV as the initial BCC phase. The stable region ranges from ‐43.87eV/nm³ to 44.06eV/nm³ in the theoretical strength or from ‐7.34% to 6.49% in the strain correspondingly. Furthermore, the relations B₁₁=B₂₂, B₁₃=B₂₃ and B₄₄=B₅₅ occur at the initial state. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of the influence of the parameters of an experiment on the simulation of pole figures of polycrystalline materials using electron microscopy

A two-dimensional mathematical model of a polycrystalline sample and an experiment on electron backscattering diffraction (EBSD) is considered. The measurement parameters are taken to be the scanning step and threshold grain-boundary angle. Discrete pole figures for materials with hexagonal symmetry have been calculated based on the results of the model experiment. Discrete and smoothed (by the kernel method) pole figures of the model sample and the samples in the model experiment are compared using homogeneity criterion χ², an estimate of the pole figure maximum and its coordinate, a deviation of the pole figures of the model in the experiment from the sample in the space of L₁ measurable functions, and the RP-criterion for estimating the pole figure errors. Is is shown that the problem of calculating pole figures is ill-posed and their determination with respect to measurement parameters is not reliable.     

电子背散衍射花样的数学特征

电子背散衍射(EBSD)花样揭示了材料的物相成分、晶体结构、晶粒取向、晶粒大小和晶界的信息。EBSD花样非常复杂,通常需要借助专门的计算软件才能解析。本文系统地研究了EBSD花样的数学特征,建立了任意晶体取向与EBSD花样之间的数理关系,推导了面心立方、体心立方和六方晶体的基本晶带轴的理论EBSD花样的数学特征,以及面心立方晶体的(001)<110>取向和(001)<100>取向的理论菊池(Kikuchi)花样特征。在实测EBSD花样的分析中与各晶系各点阵的基本晶带轴的理论EBSD花样特征比较,即通过图像特征对比,就可以直接确定实测EBSD花样所属的晶系、点阵和Kikuchi线交点对应的晶带轴[uvw],再由基本晶带轴的坐标计算出晶体取向,还能提供基本晶面信息,如原子密排晶面在样品中的空间分布,这有利于晶体的变形或生长机理研究。EBSD为单晶芯片质量检验提供了新方法。     

Effect of orientation on the microstructure of nickel‐based crystalline superalloys

The effect of crystal orientation on the microstructure of a nickel‐based crystalline superalloys during directional solidification was explored. Differently oriented crystals with [001] and [011] orientations were fabricated with seeding technique. The results showed that primary dendrite arm spacings decreased simultaneously with the increase of misroientation. The primary dendrites arrange in lines in [011] single crystal. For [001] oriented crystals, the size of γ′ phase increased with the increasing of misorientation. However, it was observed that the size of γ′ decreased with large misorientation for [011] orientated growth. Meanwhile, more γ′ in [011] crystals tended to be triangular. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and scintillating properties of (Pr,Si)‐doped YAlO3

This paper deals with Pr‐doped and Pr, Si‐codoped YAlO₃ single crystal growth by the micro‐pulling‐down method and investigation of their spectroscopic and scintillating properties. The Pr³⁺ 5d ‐4f radioluminescence intensity is more than 10 times higher than that of Bi₄Ge₃O₁₂ standard sample, but the Si‐codoping decreases it. Absorption spectra of as‐grown and air‐annealed Si,Pr‐codoped YAlO₃ samples show along with an onset of 4f ‐5d transition round 230 nm the induced absorption band at 400 nm which possibly related to a hole center absorption (Pr⁴⁺ or O^‐). Thermoluminescence measurements above the room temperature were performed in order to monitor deep electron traps. Strong concentration dependence of thermoluminescence was observed for Pr:YAlO₃ glow curves. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of mean‐separation‐works method to protein crystal nucleation

Using mean‐separation‐works method of Stranski and Kaischew calculations of nucleus form and energy barrier for its formation are performed for globular protein crystals. This is done on the basis of a simple model suggested for crystal nucleation of such proteins. The prerequisite for the model is the fact that strict selection of definite sticky patches on protein molecule surface is obligatory for forming crystal lattices. The calculation results are in agreement with experimental data. (© 2008 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Growth and Properties of the Compounds CuGa3Se5 and CuIn3Se5

CuIn₃Se₅ and CuGa₃Se₅ uniform single crystals 12 mm in diameter and 40 mm in length with the chalcopyrite‐related structure were prepared by directed crystallization of the melt. The melting points of these compounds were defined by means of the differential thermal analysis (DTA). The lattice parameters a and c as well as the axial thermal expansion coefficients α_a and α_c were determined as a function of temperature in the range from 90 to 650 K by the X‐ray diffraction method (XRD). It is found that for both the compounds the coefficients of expansion along the a ‐axis are larger than those along the c ‐axis over the entire temperature range studied.     

Melt Growth of CdTe Crystals and Transmission Electron Microscopic Investigations of their Grain Boundaries

Transmission electron microscopy investigations are carried out on CdTe crystals grown in quartz ampoules in a temperature region (1020–1091 °C) near to the melting point of 1092 °C, by travelling heater method in quasi-closed and in sealed (at 0.135 Pa) volume, and by the Bridgman method from nearly stoichiometric melts. An original method for preparation of CdTe thin foil is reported. Two types of grain boundaries are observed: high-angle misoriented grain boundaries (more than ten degrees misorientation between adjacent grains) and low-angle misoriented grain boundaries (less than one degree misorientation between adjacent sub-grain). Both dislocations with Burgers vector b = a/6 〈112〉 and b = a/2 〈110〉 are present.     

Synthesis and structure of the three‐dimensional coordination polymer [Ag3hmt3(μ3 ‐btc)]·5H2O

A new coordination polymer, [Ag₃hmt₃(μ₃ ‐btc)]·5H₂O (1) (hmt = hexamethylenetetramine, btc=1,3,5‐benzenetricarboxlic), has been successfully synthesized. Crystal data: P2₁/a, a = 11.9906(2) Å, b = 17.3689(2) Å, c = 16.96100(10) Å, β = 101.9820(14)°, V = 3455.40(7) ų, Z = 4, Dc = 2.002 Mg/m³. In the hexagonal structure of Ag‐hmt unit, each Ag‐hmt unit comprises three Ag atoms and three hmt ligands. The μ₃ ‐btc ligands bridge adjacent two‐dimensional honeycomb‐like Ag‐hmt layers to form three‐dimensional networks. Structure analysis show that hydrogen bonds play a key role for the stable structure in the compounds. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)