Investigation of orientation relationships by EBSD and EDS on the example of the Watson iron meteorite

The suitability of the electron back‐scatter diffraction technique (supported by EDS) in order to study the complex microstructures of iron meteorites is demonstrated on the example of the Watson meteorite. The orientation relationships between the main phases kamacite, taenite and schreibersite/rhabdite as well as effects of the real structure have been investigated. In kamacite bands highly deformed blocks appear which show a contineous change of orientation. Plessitic regions are surrounded by deformed taenite lamellae. Also these lamellae show the typical M‐profile of the Ni concentration in cross section. In the center a martensitic microstructure has been proven. The white plessite is characterized by a high number of individual kamacite grains which however are separated mainly by low‐angle boundaries. So an orientation clustering occurs. The determination of orientation relationships was only possible for a single plessite region comparing the intensity distribution in pole figures with simulations. Schreibersite is brittle and shows a high number of microcracks. However, the strong deformation of kamacite does not allow us to decide whether an orientation relationship between the phosphides and the surrounding kamacite exists or not. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Irrational orientation relationship derived from rational orientation relationships using EBSD data

The determination of the orientation relationship (OR) between α ‐Fe matrix (bcc) and γ ‐Fe precipitates (fcc) is discussed using orientation data collected by electron backscatter diffraction (EBSD). The comparatively low accuracy of EBSD is compensated by the high number of measurements what allows a general statement regarding to the mean OR existing in a sample. The representation and discussion is realized on a part of the Bain zone in a {001} pole figure. A discussion of some selected rational OR which are commonly used for the phase boundary characterization between α and γ shows that the pole figures describing a transformation from γ → α are different to those for α → γ. A technique is proposed based on at least three misorientation angles between the experimental OR to the rational OR's as reference. For the misorientation angle distribution a refinement is applied to extract the mean values. They are used to detect the mean OR, what is also possible for only a few or even a single precipitate if the number of measurements describing the phase boundary is sufficiently high. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron and optical microscopy studies of extraterrestrial minerals in NWA4047 meteorite

Analytical electron microscopy and optical microscopy were used to determine the elemental and mineral composition of NWA4047 meteorite. The meteorite was found in 2005 in Morocco, and in 2006 was preliminary classified as H4‐5 ordinary chondrite. The main crystalline meteorite minerals: olivines, pyroxenes, kamacite and taenite, feldspars, as well as troilite identified in our sample represent extraterrestrial minerals typical of the ordinary chondrite of high iron content. Low‐Ca orthopyroxene called bronzite has been revealed. Single enstatite and clinopyroxene crystals have also been identified. Olivines in the meteorite contain 18 mol% of fayalite. The meteorite is a monomict breccia, in which fragments of petrographic types 4, 5, and 6 are present, with the groundmass being type 4. Some of clasts contain large grains of feldspars and high content of feldspars, which is typical of petrologic type 6. Chemical and mineral composition, petrologic types of chondrules, their abundance and sizes, the presence of troilite‐kamacite veins, and nonoxidised iron phases prove that the chondrite belong to H group, i.e. to the olivine‐bronzite group. Our results show that the NWA4047 meteorite is H4‐6 ordinary chondrite. The weathering grade of the meteorite W0/1 is the same as previously established, but the shock grade S3 seems to be higher in comparison with the previous classification. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Channeling‐enhanced EDX for polarity resolved crystal orientation determination

Using channeling‐enhanced energy‐dispersive X‐ray spectroscopy (EDX), we demonstrate polarity sensitive orientation determination of a non‐centrosymmetric crystal in the scanning electron microscope. The authors observe a characteristic asymmetry in the channeling‐enhanced, angle‐dependent EDX data of a GaAs sample, which is in good agreement to simulations using the dynamical theory of diffraction for the incident electron beam. This allows us to assign the orientation of the GaAs crystal according to the non‐centrosymmetric point group. The method shown here overcomes the limitation of a reduced point‐group sensitivity of electron backscatter diffraction patterns and electron channeling patterns for crystalline phases that contain atoms of approximately equal electron scattering cross sections.     

Crystallographic shear defect in molybdenum oxides: Structure and TEM of molybdenum sub‐oxides Mo18O52 and Mo8O23

Molybdenum trioxide and molybdenum sub‐oxides are of great interests in catalysis due to their utilities as model system to elucidate the correlations between the structure and the catalytic performance. The suboxides are usually an intermediate phase during catalytic reaction in which the lattice oxygen is involved. We show the identification of the two common molybdenum sub‐oxides Mo₁₈O₅₂ and Mo₈O₂₃, derived from MoO₃ by crystallographic shearing (CS), by means of electron diffraction and High‐Resolution Transmission Electron Microscopy (HRTEM) in combination with image simulation. The coincidence of simulated electron diffraction patterns and high‐resolution images with the experimental ones indicates the feasibility of CS structure determination by these techniques.     

Investigation of the accuracy of modeling the orientation distribution function of polycrystalline materials from individual orientations

The accuracy of reconstructing the orientation distribution function of grains in polycrystalline materials by the kernel method from a set of individual orientations has been studied. In particular, the influence of choosing the smoothing kernel in the kernel method and the influence of the dependence on the resulting distribution are taken into account. The rotations obeying the normal distribution on the group SO(3) and obtained by the statistical test method are used as an orientation set. Some aspects of electron backscattering diffraction measurements are considered. This problem is urgent in view of the expanding potential of the experimental study of the texture of polycrystalline materials, especially for electron microscopy, which makes it possible to measure the orientations of individual grains.     

Growth and characterization of highly c‐axis textured SrTiO3 thin films directly grown on Si(001) substrates by ion beam sputter deposition

Highly c‐axis textured SrTiO₃ (STO) thin films have been directly grown on Si(001) substrates using ion beam sputter deposition technique without any buffer layer. The substrate temperature was varied, while other parameters were fixed in order to study effect of substrate temperature on morphology and texture evolution of STO films. X‐ray diffraction, pole figure analysis, atomic force microscope, and high‐resolution electron microscopy were used to characterize and confirm quality and texture of the STO films. The experimental results show that optimum substrate temperature to achieve highly c‐axis textured films is at 700 °C. The full width at half maximum (FWHM) of 002_STO was found to be 2° and fraction of (011) orientation was as low as 1%. The surface morphology was Volmer‐Weber growth mode with a small roughness ∼1 nm. The lowest leakage current density (5.8 μA/cm² at 2 V) and the highest dielectric constant (ε_STO ∼ 98) were found for highly c‐axis textured films grown at 700 °C. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zr‐doped CeO2 Hollow slightly‐truncated nano‐octahedrons: One‐pot synthesis,characterization and their application in catalysis of CO oxidation

Zirconium‐doped ceria hollow slightly‐truncated nano‐octahedrons (HTNOs) (Ce_1‐xZr_xO₂) were synthesized by a one‐pot, facile hydrothermal method. The morphology and crystalline structure were characterized with powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and the high resolution transmission electron microscopy (HRTEM). The composition and chemical valence on the surface of the as‐prepared Ce_1‐xZr_xO₂ powders were detected by X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The surface area and pore size distribution of as‐obtained Zr‐doped ceria HTNOs were measured by N₂ adsorption‐desorption measurement. Mechanisms for the growth of Zr‐doped ceria HTNOs are proposed as both oriented attachment and Ostwald ripening process and the formation of the hollow structure is strongly dependent on the addition of Zr⁴⁺ ions. Furthermore, the as‐obtained Zr‐doped ceria HTNOs revealed superior catalytic activity and thermal stability toward CO oxidation compared to pure ceria. It may provide a new path for the fabrication of inorganic hollow structures on introducing alien metal ions.     

Synthesis of spindle‐shaped α‐FeOOH and α‐Fe2O3 nanocrystals

Spindle‐shaped α‐FeOOH nanocrystals were facilely synthesized using a poly (vinyl pyrrolidone) (PVP)‐assisted route under hydrothermal conditions. The chemical compositions and morphol‐ogies of the as‐prepared samples were characterized in detail by X‐ray power diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The experimental results reveal that these spindle‐shaped α‐FeOOH nanocrystals have self‐organized into assemblies with hierarchical nanostructures. The crucial roles of PVP in the hydrothermal synthesis of hierarchical α‐FeOOH nanostructures were discussed. The possible formation mechanism was also suggested. Moreover, the spindle‐shaped α‐Fe₂O₃ nanocrystals could be easily obtained after calcining the α‐FeOOH prepared by the PVP‐assisted hydrothermal process. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Complex boron redistribution kinetics in strongly doped polycrystalline‐silicon/nitrogen‐doped‐silicon thin bi‐layers

We have investigated the complex behaviour of boron (B) redistribution process via silicon thin bi‐layers interface. It concerns the instantaneous kinetics of B transfer, trapping, clustering and segregation during the thermal B activation annealing. The used silicon bi‐layers have been obtained by low pressure chemical vapor deposition (LPCVD) method at 480 °C, by using in‐situ nitrogen‐doped‐silicon (NiDoS) layer and strongly B doped polycrystalline‐silicon (P⁺) layer. To avoid long‐range B redistributions, thermal annealing was carried out at relatively low‐temperatures (600 °C and 700 °C) for various times ranging between 30 min and 2 h. To investigate the experimental secondary ion mass spectroscopy (SIMS) doping profiles, a redistribution model well adapted to the particular structure of two thin layers and to the effects of strong‐concentrations has been established. The good adjustment of the simulated profiles with the experimental SIMS profiles allowed a fundamental understanding about the instantaneous physical phenomena giving and disturbing the complex B redistribution profiles‐shoulders. The increasing kinetics of the B peak concentration near the bi‐layers interface is well reproduced by the established model.     

Nd(III) and Yb(III) ions incorporated in Y4Al2O9 obtained by sol‐gel method: synthesis,structure, crystals and luminescence

The nanocrystalline powders of Y₄Al₂O₉ (YAM) pure and doped by Nd, Yb and codoped by Nd and Yb were obtained via modified sol‐gel method. These powders were characterized by X‐ray diffraction method, scanning electron microscopy and high resolution scanning electron microscopy, luminescence spectroscopy and differential thermal analysis (DTA). We obtained single phase powders of crystalline structure with average size 70 nm exhibiting interesting luminescent properties. Efficient non‐radiative energy transfer between Nd and Yb was found. DTA confirmed the phase transition at about 1400 °C. From these nanocrystalline powders, the crystals YAM:Yb, YAM:Yb,Nd were grown by micro‐pulling down technique. They were cracking during cooling owing to the phase transition. Luminescent properties of YAM:Nd,Yb crystals were identical with properties of corresponding nanopowders within experimental incertitude. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Probabilistic electron density distribution in CdTe at RT and 200K

The bonding between the atoms in the II‐VI compound semiconductors has always been a subject of rigorous research because of their tremendous applications in a variety of fields. The bonding and ionic character in CdTe at 300 and 200 K have been determined quantitatively as well as qualitatively using single crystal X‐ray data sets and MEM (Maximum Entropy Method) as the tool for the reconstruction of the electron densities distributed within the unit cell. The ab‐initio band calculation of the total and valence charge densities have been carried out theoretically by means of the local density approximation (LDA) method in support of the experimentally derived MEM maps. The difference density maps show fewer errors between the theoretical and experimental charge density and thus gives credence to the results accordingly. Along the bonding direction [111], the mid‐bond electron densities are found to be 0.233 e/ų and 0.284 e/ų at 300 K and 200 K at distances 1.4026 Å and 1.4036 Å respectively. The densities along [100] and [110] show an increase in the charge concentration at the bond at lower temperatures. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Atomic‐scale study of vapour growth morphology of crystalline urea

The role of surface relaxation on habit controlling energetics and growth morphology are investigated within the framework of Burton‐Cabrera‐Frank (BCF) and Hartman‐Perdok (HP) models. The habit controlling energetics has been calculated using first principles method. The growth morphology obtained using BCF theory shows that the structural relaxation has considerable effect on growth morphology. The relaxed growth morphology obtained using BCF model match with the experimental result from vapour phase. On the other hand the shape obtained using HP model does not correspond with the experimental shape. Observed polar growth morphology of urea crystal has been discussed particularly in the context of different atomic environments of (111) and (111) faces. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Systematic,properties, and structure predictions of new borate materials

New borates with the non‐linear optical properties, obtained and investigated in Moscow State University in the last years, are reviewed. The positions of compounds in systematic were determined including complicate cases using topology and symmetry analysis of anionic radicals with the separation of blocks, typical for borate groups. Such approach revealed structural correlations between borates and silicates and led to prediction of new structures, two of which are realized. The origin of properties is connected with the highly polarizable electron density on lone pair or asymmetric bonds, presented in the structures. Experimental observation electron density distrubution has been made for Pb‐hilgardite, a crystal with the high optical non‐linearity. Different approaches to the structure‐properties relation are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spontaneous crystallization of potassium chloride from aqueous and aqueous‐ethanol solutions; Part 3: Model of the crystallization process

A model of spontaneous crystallization process was proposed. The model describes kinetics of the crystallization process after the end of the induction period. To test the model the published earlier data on crystallization and aggregation kinetics of potassium chloride at its spontaneous crystallization from supersaturated aqueous and aqueous‐ethanol solutions were used. It was found excellent coincidence of the experimental and theoretical data on concentration of the salt and the total number of crystals in solution at crystallization. Somewhat change for the worse was at the theoretical calculations of crystal size distribution at the end of the crystallization process. It indicated that the ways of calculation of size of crystals and their weight fraction in deposit were very approximate. The model allows predicting with satisfactory accuracy kinetics of crystallization using such general parameters of potassium chloride as the specific surface energy and the height of the nucleus‐bridges between crystals at coalescence. It needs further test of the model for other salts. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influence of substrate temperature on the growth of sexiphenyl on mica(001)

Sexiphenyl thin films were grown by Hot Wall Epitaxy on air‐cleaved mica (001) surfaces at substrate temperatures between 293 K and 440 K. For the entire temperature range, organic thin films show nano‐needle like morphology. The nano‐needles grown at low substrate temperature (293 K) are shortest, and their growth is accompanied by a simultaneous formation of flat islands which disturbs the growth of nano‐needles. On the contrary, unusually long nano‐needles with typical lengths up to the mm range evolve during the growth at a substrate temperature close to the material's thermal desorption temperature at about 440 K. X‐ray diffraction reveals two different crystalline orientations for nano‐needles in the entire temperature range. At low substrate temperatures dominantly the (11 ) plane of the β‐phase is formed parallel to the mica (001) surface. At elevated temperatures another strong texture becomes dominant which is close to the (11 ) crystal orientation. In contrast to this, crystallites with the preferred orientation (001) parallel to the surface of the substrate are formed at low substrate temperature (293 K). This crystal orientation can be associated with flat islands observed in the early growth stage. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation on defects in Lu2SiO5:Ce crystals grown by Czochralski method

Cerium‐doped lutetium oxyorthosilicate crystals (Lu₂SiO₅:Ce) with dimension of ∅︁50 × 60 mm were grown by Czochralski method from an inductively heated iridium crucible. The vaporized substance during growth was examined with XRD and proved to be SiO₂. The vertical and the screw strips existing on the surface of the boule were observed with optical microscope and tested with electron microprobe. They are confirmed to be iridium from the crucible and harmful to the crystal growth. The cleavage orientation of LSO was proved to be (110) and it is one of factors to cause crystal cracking. The scattering particles in LSO crystals are analyzed to be mainly composed of Lu₂O₃ inclusions. Two possible origins on these inclusions are proposed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of SrMoO4 microstructures by the microwave radiation‐assisted chelating agent method

SrMoO₄ rose‐like and persimmon‐like structures were synthesized via microwave radiation‐assisted chelating agent method. The microstructure and morphology of the as‐prepared samples were analyzed by X‐ray diffraction and field‐emission scanning electron microscope. According to the experimental results, ethylenediaminetetraacetic acid, as an outstanding chelating agent, plays an important role in inducing the morphology evolution. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and structural analysis of angled Te nanocrystals

In this paper, a new direct method to prepare angled Te nanocrystals (NCs) in the isotropic thiol‐ligand system from the transformation of MA‐stabilized CdTe nanoparticles (NPs) induced by the post‐addition of L‐cysteine was presented, without removing aforehand the protective shell of organic stabilizer. Besides nanorods, angled Te nanocrystals, including nanocheckmarks, X‐shaped, nanomoths, y‐shaped, and so on, also were obtained. By means of high‐resolution transmission electron microscopy (HRTEM), selected‐area electron diffraction (SAED) and powder X‐ray diffractometry (XRD), we further investigated intensively the internal crystal structure of angled Te NCs and the growth direction of the arms in this study. The experimental results obtained show that the preferential growth direction of either arms in nanocheckmarks is along the [001] direction of trigonal Te, and the corresponding contact plane should be (112) of hexagonal lattice. In the meantime, these results also confirm that L‐cysteine not only can be used as the stabilizer for the synthesis of aqueous CdTe NPs as reported previously, but also can act as a strong complexing agent like EDTA, inducing the decomposition of CdTe NPs, i.e. the transformation from CdTe NPs to Te nanocrystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,microchemical and superconducting properties of ultrathin NbN films on silicon

Structural, chemical and superconducting properties of thin NbN films used for development of fast and sensitive hot‐electron bolometer (HEB) detectors for wide spectra range are reported. The thin NbN films with a thickness between 4 and 10 nm were deposited on the (001)Si substrates by magnetron sputtering. In order to investigate the film morphology and microchemistry, diffraction‐contrast and high‐resolution transmission electron microscopy (TEM) in combination with scanning TEM and electron energy loss spectroscopy (EELS) were performed. In addition, the zero‐resistance critical temperature of the NbN films was measured and correlated to their thickness. The interrelations between fabrication conditions, crystalline and superconducting properties of the differently thick NbN films are discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)